1 //===-- runtime/unit.cpp ----------------------------------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #include "unit.h"
10 #include "environment.h"
11 #include "io-error.h"
12 #include "lock.h"
13 #include "unit-map.h"
14 #include <cstdio>
15 #include <limits>
16 #include <utility>
17 
18 namespace Fortran::runtime::io {
19 
20 // The per-unit data structures are created on demand so that Fortran I/O
21 // should work without a Fortran main program.
22 static Lock unitMapLock;
23 static UnitMap *unitMap{nullptr};
24 static ExternalFileUnit *defaultInput{nullptr};
25 static ExternalFileUnit *defaultOutput{nullptr};
26 
27 void FlushOutputOnCrash(const Terminator &terminator) {
28   if (!defaultOutput) {
29     return;
30   }
31   CriticalSection critical{unitMapLock};
32   if (defaultOutput) {
33     IoErrorHandler handler{terminator};
34     handler.HasIoStat(); // prevent nested crash if flush has error
35     defaultOutput->FlushOutput(handler);
36   }
37 }
38 
39 ExternalFileUnit *ExternalFileUnit::LookUp(int unit) {
40   return GetUnitMap().LookUp(unit);
41 }
42 
43 ExternalFileUnit &ExternalFileUnit::LookUpOrCrash(
44     int unit, const Terminator &terminator) {
45   ExternalFileUnit *file{LookUp(unit)};
46   if (!file) {
47     terminator.Crash("Not an open I/O unit number: %d", unit);
48   }
49   return *file;
50 }
51 
52 ExternalFileUnit &ExternalFileUnit::LookUpOrCreate(
53     int unit, const Terminator &terminator, bool &wasExtant) {
54   return GetUnitMap().LookUpOrCreate(unit, terminator, wasExtant);
55 }
56 
57 ExternalFileUnit &ExternalFileUnit::LookUpOrCreateAnonymous(int unit,
58     Direction dir, std::optional<bool> isUnformatted,
59     const Terminator &terminator) {
60   bool exists{false};
61   ExternalFileUnit &result{
62       GetUnitMap().LookUpOrCreate(unit, terminator, exists)};
63   if (!exists) {
64     IoErrorHandler handler{terminator};
65     result.OpenAnonymousUnit(
66         dir == Direction::Input ? OpenStatus::Unknown : OpenStatus::Replace,
67         Action::ReadWrite, Position::Rewind, Convert::Native, handler);
68     result.isUnformatted = isUnformatted;
69   }
70   return result;
71 }
72 
73 ExternalFileUnit *ExternalFileUnit::LookUp(const char *path) {
74   return GetUnitMap().LookUp(path);
75 }
76 
77 ExternalFileUnit &ExternalFileUnit::CreateNew(
78     int unit, const Terminator &terminator) {
79   bool wasExtant{false};
80   ExternalFileUnit &result{
81       GetUnitMap().LookUpOrCreate(unit, terminator, wasExtant)};
82   RUNTIME_CHECK(terminator, !wasExtant);
83   return result;
84 }
85 
86 ExternalFileUnit *ExternalFileUnit::LookUpForClose(int unit) {
87   return GetUnitMap().LookUpForClose(unit);
88 }
89 
90 ExternalFileUnit &ExternalFileUnit::NewUnit(
91     const Terminator &terminator, bool forChildIo) {
92   ExternalFileUnit &unit{GetUnitMap().NewUnit(terminator)};
93   unit.createdForInternalChildIo_ = forChildIo;
94   return unit;
95 }
96 
97 void ExternalFileUnit::OpenUnit(std::optional<OpenStatus> status,
98     std::optional<Action> action, Position position, OwningPtr<char> &&newPath,
99     std::size_t newPathLength, Convert convert, IoErrorHandler &handler) {
100   if (executionEnvironment.conversion != Convert::Unknown) {
101     convert = executionEnvironment.conversion;
102   }
103   swapEndianness_ = convert == Convert::Swap ||
104       (convert == Convert::LittleEndian && !isHostLittleEndian) ||
105       (convert == Convert::BigEndian && isHostLittleEndian);
106   if (IsOpen()) {
107     bool isSamePath{newPath.get() && path() && pathLength() == newPathLength &&
108         std::memcmp(path(), newPath.get(), newPathLength) == 0};
109     if (status && *status != OpenStatus::Old && isSamePath) {
110       handler.SignalError("OPEN statement for connected unit may not have "
111                           "explicit STATUS= other than 'OLD'");
112       return;
113     }
114     if (!newPath.get() || isSamePath) {
115       // OPEN of existing unit, STATUS='OLD' or unspecified, not new FILE=
116       newPath.reset();
117       return;
118     }
119     // Otherwise, OPEN on open unit with new FILE= implies CLOSE
120     DoImpliedEndfile(handler);
121     FlushOutput(handler);
122     Close(CloseStatus::Keep, handler);
123   }
124   set_path(std::move(newPath), newPathLength);
125   Open(status.value_or(OpenStatus::Unknown), action, position, handler);
126   auto totalBytes{knownSize()};
127   if (access == Access::Direct) {
128     if (!isFixedRecordLength || !recordLength) {
129       handler.SignalError(IostatOpenBadRecl,
130           "OPEN(UNIT=%d,ACCESS='DIRECT'): record length is not known",
131           unitNumber());
132     } else if (*recordLength <= 0) {
133       handler.SignalError(IostatOpenBadRecl,
134           "OPEN(UNIT=%d,ACCESS='DIRECT',RECL=%jd): record length is invalid",
135           unitNumber(), static_cast<std::intmax_t>(*recordLength));
136     } else if (totalBytes && (*totalBytes % *recordLength != 0)) {
137       handler.SignalError(IostatOpenBadAppend,
138           "OPEN(UNIT=%d,ACCESS='DIRECT',RECL=%jd): record length is not an "
139           "even divisor of the file size %jd",
140           unitNumber(), static_cast<std::intmax_t>(*recordLength),
141           static_cast<std::intmax_t>(*totalBytes));
142     }
143   }
144   endfileRecordNumber.reset();
145   currentRecordNumber = 1;
146   if (totalBytes && recordLength && *recordLength) {
147     endfileRecordNumber = 1 + (*totalBytes / *recordLength);
148   }
149   if (position == Position::Append) {
150     if (!endfileRecordNumber) {
151       // Fake it so that we can backspace relative from the end
152       endfileRecordNumber = std::numeric_limits<std::int64_t>::max() - 2;
153     }
154     currentRecordNumber = *endfileRecordNumber;
155   }
156 }
157 
158 void ExternalFileUnit::OpenAnonymousUnit(std::optional<OpenStatus> status,
159     std::optional<Action> action, Position position, Convert convert,
160     IoErrorHandler &handler) {
161   // I/O to an unconnected unit reads/creates a local file, e.g. fort.7
162   std::size_t pathMaxLen{32};
163   auto path{SizedNew<char>{handler}(pathMaxLen)};
164   std::snprintf(path.get(), pathMaxLen, "fort.%d", unitNumber_);
165   OpenUnit(status, action, position, std::move(path), std::strlen(path.get()),
166       convert, handler);
167 }
168 
169 void ExternalFileUnit::CloseUnit(CloseStatus status, IoErrorHandler &handler) {
170   DoImpliedEndfile(handler);
171   FlushOutput(handler);
172   Close(status, handler);
173 }
174 
175 void ExternalFileUnit::DestroyClosed() {
176   GetUnitMap().DestroyClosed(*this); // destroys *this
177 }
178 
179 bool ExternalFileUnit::SetDirection(
180     Direction direction, IoErrorHandler &handler) {
181   if (direction == Direction::Input) {
182     if (mayRead()) {
183       direction_ = Direction::Input;
184       return true;
185     } else {
186       handler.SignalError(IostatReadFromWriteOnly,
187           "READ(UNIT=%d) with ACTION='WRITE'", unitNumber());
188       return false;
189     }
190   } else {
191     if (mayWrite()) {
192       direction_ = Direction::Output;
193       return true;
194     } else {
195       handler.SignalError(IostatWriteToReadOnly,
196           "WRITE(UNIT=%d) with ACTION='READ'", unitNumber());
197       return false;
198     }
199   }
200 }
201 
202 UnitMap &ExternalFileUnit::GetUnitMap() {
203   if (unitMap) {
204     return *unitMap;
205   }
206   CriticalSection critical{unitMapLock};
207   if (unitMap) {
208     return *unitMap;
209   }
210   Terminator terminator{__FILE__, __LINE__};
211   IoErrorHandler handler{terminator};
212   UnitMap *newUnitMap{New<UnitMap>{terminator}().release()};
213   bool wasExtant{false};
214   ExternalFileUnit &out{newUnitMap->LookUpOrCreate(6, terminator, wasExtant)};
215   RUNTIME_CHECK(terminator, !wasExtant);
216   out.Predefine(1);
217   out.SetDirection(Direction::Output, handler);
218   defaultOutput = &out;
219   ExternalFileUnit &in{newUnitMap->LookUpOrCreate(5, terminator, wasExtant)};
220   RUNTIME_CHECK(terminator, !wasExtant);
221   in.Predefine(0);
222   in.SetDirection(Direction::Input, handler);
223   defaultInput = &in;
224   // TODO: Set UTF-8 mode from the environment
225   unitMap = newUnitMap;
226   return *unitMap;
227 }
228 
229 void ExternalFileUnit::CloseAll(IoErrorHandler &handler) {
230   CriticalSection critical{unitMapLock};
231   if (unitMap) {
232     unitMap->CloseAll(handler);
233     FreeMemoryAndNullify(unitMap);
234   }
235   defaultOutput = nullptr;
236 }
237 
238 void ExternalFileUnit::FlushAll(IoErrorHandler &handler) {
239   CriticalSection critical{unitMapLock};
240   if (unitMap) {
241     unitMap->FlushAll(handler);
242   }
243 }
244 
245 static void SwapEndianness(
246     char *data, std::size_t bytes, std::size_t elementBytes) {
247   if (elementBytes > 1) {
248     auto half{elementBytes >> 1};
249     for (std::size_t j{0}; j + elementBytes <= bytes; j += elementBytes) {
250       for (std::size_t k{0}; k < half; ++k) {
251         std::swap(data[j + k], data[j + elementBytes - 1 - k]);
252       }
253     }
254   }
255 }
256 
257 bool ExternalFileUnit::Emit(const char *data, std::size_t bytes,
258     std::size_t elementBytes, IoErrorHandler &handler) {
259   auto furthestAfter{std::max(furthestPositionInRecord,
260       positionInRecord + static_cast<std::int64_t>(bytes))};
261   if (furthestAfter > recordLength.value_or(furthestAfter)) {
262     handler.SignalError(IostatRecordWriteOverrun,
263         "Attempt to write %zd bytes to position %jd in a fixed-size record of "
264         "%jd bytes",
265         bytes, static_cast<std::intmax_t>(positionInRecord),
266         static_cast<std::intmax_t>(*recordLength));
267     return false;
268   }
269   WriteFrame(frameOffsetInFile_, recordOffsetInFrame_ + furthestAfter, handler);
270   if (positionInRecord > furthestPositionInRecord) {
271     std::memset(Frame() + recordOffsetInFrame_ + furthestPositionInRecord, ' ',
272         positionInRecord - furthestPositionInRecord);
273   }
274   char *to{Frame() + recordOffsetInFrame_ + positionInRecord};
275   std::memcpy(to, data, bytes);
276   if (swapEndianness_) {
277     SwapEndianness(to, bytes, elementBytes);
278   }
279   positionInRecord += bytes;
280   furthestPositionInRecord = furthestAfter;
281   return true;
282 }
283 
284 bool ExternalFileUnit::Receive(char *data, std::size_t bytes,
285     std::size_t elementBytes, IoErrorHandler &handler) {
286   RUNTIME_CHECK(handler, direction_ == Direction::Input);
287   auto furthestAfter{std::max(furthestPositionInRecord,
288       positionInRecord + static_cast<std::int64_t>(bytes))};
289   if (furthestAfter > recordLength.value_or(furthestAfter)) {
290     handler.SignalError(IostatRecordReadOverrun,
291         "Attempt to read %zd bytes at position %jd in a record of %jd bytes",
292         bytes, static_cast<std::intmax_t>(positionInRecord),
293         static_cast<std::intmax_t>(*recordLength));
294     return false;
295   }
296   auto need{recordOffsetInFrame_ + furthestAfter};
297   auto got{ReadFrame(frameOffsetInFile_, need, handler)};
298   if (got >= need) {
299     std::memcpy(data, Frame() + recordOffsetInFrame_ + positionInRecord, bytes);
300     if (swapEndianness_) {
301       SwapEndianness(data, bytes, elementBytes);
302     }
303     positionInRecord += bytes;
304     furthestPositionInRecord = furthestAfter;
305     return true;
306   } else {
307     // EOF or error: can be handled & has been signaled
308     endfileRecordNumber = currentRecordNumber;
309     return false;
310   }
311 }
312 
313 std::optional<char32_t> ExternalFileUnit::GetCurrentChar(
314     IoErrorHandler &handler) {
315   RUNTIME_CHECK(handler, direction_ == Direction::Input);
316   if (const char *p{FrameNextInput(handler, 1)}) {
317     // TODO: UTF-8 decoding; may have to get more bytes in a loop
318     return *p;
319   }
320   return std::nullopt;
321 }
322 
323 const char *ExternalFileUnit::FrameNextInput(
324     IoErrorHandler &handler, std::size_t bytes) {
325   RUNTIME_CHECK(handler, isUnformatted.has_value() && !*isUnformatted);
326   if (static_cast<std::int64_t>(positionInRecord + bytes) <=
327       recordLength.value_or(positionInRecord + bytes)) {
328     auto at{recordOffsetInFrame_ + positionInRecord};
329     auto need{static_cast<std::size_t>(at + bytes)};
330     auto got{ReadFrame(frameOffsetInFile_, need, handler)};
331     SetSequentialVariableFormattedRecordLength();
332     if (got >= need) {
333       return Frame() + at;
334     }
335     handler.SignalEnd();
336     endfileRecordNumber = currentRecordNumber;
337   }
338   return nullptr;
339 }
340 
341 bool ExternalFileUnit::SetSequentialVariableFormattedRecordLength() {
342   if (recordLength || access != Access::Sequential) {
343     return true;
344   } else if (FrameLength() > recordOffsetInFrame_) {
345     const char *record{Frame() + recordOffsetInFrame_};
346     std::size_t bytes{FrameLength() - recordOffsetInFrame_};
347     if (const char *nl{
348             reinterpret_cast<const char *>(std::memchr(record, '\n', bytes))}) {
349       recordLength = nl - record;
350       if (*recordLength > 0 && record[*recordLength - 1] == '\r') {
351         --*recordLength;
352       }
353     } else {
354       recordLength = bytes; // final record w/o \n
355     }
356     return true;
357   } else {
358     return false;
359   }
360 }
361 
362 void ExternalFileUnit::SetLeftTabLimit() {
363   leftTabLimit = furthestPositionInRecord;
364   positionInRecord = furthestPositionInRecord;
365 }
366 
367 bool ExternalFileUnit::BeginReadingRecord(IoErrorHandler &handler) {
368   RUNTIME_CHECK(handler, direction_ == Direction::Input);
369   if (!beganReadingRecord_) {
370     beganReadingRecord_ = true;
371     if (access == Access::Sequential) {
372       if (endfileRecordNumber && currentRecordNumber >= *endfileRecordNumber) {
373         handler.SignalEnd();
374       } else if (isFixedRecordLength) {
375         RUNTIME_CHECK(handler, recordLength.has_value());
376         auto need{
377             static_cast<std::size_t>(recordOffsetInFrame_ + *recordLength)};
378         auto got{ReadFrame(frameOffsetInFile_, need, handler)};
379         if (got < need) {
380           handler.SignalEnd();
381         }
382       } else {
383         RUNTIME_CHECK(handler, isUnformatted.has_value());
384         if (isUnformatted.value_or(false)) {
385           BeginSequentialVariableUnformattedInputRecord(handler);
386         } else { // formatted
387           BeginSequentialVariableFormattedInputRecord(handler);
388         }
389       }
390     }
391   }
392   RUNTIME_CHECK(handler,
393       access != Access::Sequential || recordLength.has_value() ||
394           handler.InError());
395   return !handler.InError();
396 }
397 
398 void ExternalFileUnit::FinishReadingRecord(IoErrorHandler &handler) {
399   RUNTIME_CHECK(handler, direction_ == Direction::Input && beganReadingRecord_);
400   beganReadingRecord_ = false;
401   if (handler.InError()) {
402     // avoid bogus crashes in END/ERR circumstances
403   } else if (access == Access::Sequential) {
404     RUNTIME_CHECK(handler, recordLength.has_value());
405     if (isFixedRecordLength) {
406       frameOffsetInFile_ += recordOffsetInFrame_ + *recordLength;
407       recordOffsetInFrame_ = 0;
408     } else {
409       RUNTIME_CHECK(handler, isUnformatted.has_value());
410       if (isUnformatted.value_or(false)) {
411         // Retain footer in frame for more efficient BACKSPACE
412         frameOffsetInFile_ += recordOffsetInFrame_ + *recordLength;
413         recordOffsetInFrame_ = sizeof(std::uint32_t);
414         recordLength.reset();
415       } else { // formatted
416         if (FrameLength() > recordOffsetInFrame_ + *recordLength &&
417             Frame()[recordOffsetInFrame_ + *recordLength] == '\r') {
418           ++recordOffsetInFrame_;
419         }
420         if (FrameLength() >= recordOffsetInFrame_ &&
421             Frame()[recordOffsetInFrame_ + *recordLength] == '\n') {
422           ++recordOffsetInFrame_;
423         }
424         recordOffsetInFrame_ += *recordLength;
425         recordLength.reset();
426       }
427     }
428   }
429   ++currentRecordNumber;
430   BeginRecord();
431 }
432 
433 bool ExternalFileUnit::AdvanceRecord(IoErrorHandler &handler) {
434   if (direction_ == Direction::Input) {
435     FinishReadingRecord(handler);
436     return BeginReadingRecord(handler);
437   } else { // Direction::Output
438     bool ok{true};
439     RUNTIME_CHECK(handler, isUnformatted.has_value());
440     if (isFixedRecordLength && recordLength) {
441       // Pad remainder of fixed length record
442       if (furthestPositionInRecord < *recordLength) {
443         WriteFrame(
444             frameOffsetInFile_, recordOffsetInFrame_ + *recordLength, handler);
445         std::memset(Frame() + recordOffsetInFrame_ + furthestPositionInRecord,
446             isUnformatted.value_or(false) ? 0 : ' ',
447             *recordLength - furthestPositionInRecord);
448       }
449     } else {
450       positionInRecord = furthestPositionInRecord;
451       if (isUnformatted.value_or(false)) {
452         // Append the length of a sequential unformatted variable-length record
453         // as its footer, then overwrite the reserved first four bytes of the
454         // record with its length as its header.  These four bytes were skipped
455         // over in BeginUnformattedIO<Output>().
456         // TODO: Break very large records up into subrecords with negative
457         // headers &/or footers
458         std::uint32_t length;
459         length = furthestPositionInRecord - sizeof length;
460         ok = ok &&
461             Emit(reinterpret_cast<const char *>(&length), sizeof length,
462                 sizeof length, handler);
463         positionInRecord = 0;
464         ok = ok &&
465             Emit(reinterpret_cast<const char *>(&length), sizeof length,
466                 sizeof length, handler);
467       } else {
468         // Terminate formatted variable length record
469         ok = ok && Emit("\n", 1, 1, handler); // TODO: Windows CR+LF
470       }
471     }
472     CommitWrites();
473     impliedEndfile_ = true;
474     ++currentRecordNumber;
475     if (endfileRecordNumber && currentRecordNumber >= *endfileRecordNumber) {
476       endfileRecordNumber.reset();
477     }
478     return ok;
479   }
480 }
481 
482 void ExternalFileUnit::BackspaceRecord(IoErrorHandler &handler) {
483   if (access != Access::Sequential) {
484     handler.SignalError(IostatBackspaceNonSequential,
485         "BACKSPACE(UNIT=%d) on non-sequential file", unitNumber());
486   } else {
487     if (endfileRecordNumber && currentRecordNumber > *endfileRecordNumber) {
488       // BACKSPACE after explicit ENDFILE
489       currentRecordNumber = *endfileRecordNumber;
490     } else {
491       DoImpliedEndfile(handler);
492       if (frameOffsetInFile_ + recordOffsetInFrame_ > 0) {
493         --currentRecordNumber;
494         if (isFixedRecordLength) {
495           BackspaceFixedRecord(handler);
496         } else {
497           RUNTIME_CHECK(handler, isUnformatted.has_value());
498           if (isUnformatted.value_or(false)) {
499             BackspaceVariableUnformattedRecord(handler);
500           } else {
501             BackspaceVariableFormattedRecord(handler);
502           }
503         }
504       }
505     }
506     BeginRecord();
507   }
508 }
509 
510 void ExternalFileUnit::FlushOutput(IoErrorHandler &handler) {
511   if (!mayPosition()) {
512     auto frameAt{FrameAt()};
513     if (frameOffsetInFile_ >= frameAt &&
514         frameOffsetInFile_ <
515             static_cast<std::int64_t>(frameAt + FrameLength())) {
516       // A Flush() that's about to happen to a non-positionable file
517       // needs to advance frameOffsetInFile_ to prevent attempts at
518       // impossible seeks
519       CommitWrites();
520     }
521   }
522   Flush(handler);
523 }
524 
525 void ExternalFileUnit::FlushIfTerminal(IoErrorHandler &handler) {
526   if (isTerminal()) {
527     FlushOutput(handler);
528   }
529 }
530 
531 void ExternalFileUnit::Endfile(IoErrorHandler &handler) {
532   if (access != Access::Sequential) {
533     handler.SignalError(IostatEndfileNonSequential,
534         "ENDFILE(UNIT=%d) on non-sequential file", unitNumber());
535   } else if (!mayWrite()) {
536     handler.SignalError(IostatEndfileUnwritable,
537         "ENDFILE(UNIT=%d) on read-only file", unitNumber());
538   } else if (endfileRecordNumber &&
539       currentRecordNumber > *endfileRecordNumber) {
540     // ENDFILE after ENDFILE
541   } else {
542     DoEndfile(handler);
543     // Explicit ENDFILE leaves position *after* the endfile record
544     RUNTIME_CHECK(handler, endfileRecordNumber.has_value());
545     currentRecordNumber = *endfileRecordNumber + 1;
546   }
547 }
548 
549 void ExternalFileUnit::Rewind(IoErrorHandler &handler) {
550   if (access == Access::Direct) {
551     handler.SignalError(IostatRewindNonSequential,
552         "REWIND(UNIT=%d) on non-sequential file", unitNumber());
553   } else {
554     DoImpliedEndfile(handler);
555     SetPosition(0);
556     currentRecordNumber = 1;
557   }
558 }
559 
560 void ExternalFileUnit::EndIoStatement() {
561   io_.reset();
562   u_.emplace<std::monostate>();
563   lock_.Drop();
564 }
565 
566 void ExternalFileUnit::BeginSequentialVariableUnformattedInputRecord(
567     IoErrorHandler &handler) {
568   std::int32_t header{0}, footer{0};
569   std::size_t need{recordOffsetInFrame_ + sizeof header};
570   std::size_t got{ReadFrame(frameOffsetInFile_, need, handler)};
571   // Try to emit informative errors to help debug corrupted files.
572   const char *error{nullptr};
573   if (got < need) {
574     if (got == recordOffsetInFrame_) {
575       handler.SignalEnd();
576     } else {
577       error = "Unformatted variable-length sequential file input failed at "
578               "record #%jd (file offset %jd): truncated record header";
579     }
580   } else {
581     std::memcpy(&header, Frame() + recordOffsetInFrame_, sizeof header);
582     recordLength = sizeof header + header; // does not include footer
583     need = recordOffsetInFrame_ + *recordLength + sizeof footer;
584     got = ReadFrame(frameOffsetInFile_, need, handler);
585     if (got < need) {
586       error = "Unformatted variable-length sequential file input failed at "
587               "record #%jd (file offset %jd): hit EOF reading record with "
588               "length %jd bytes";
589     } else {
590       std::memcpy(&footer, Frame() + recordOffsetInFrame_ + *recordLength,
591           sizeof footer);
592       if (footer != header) {
593         error = "Unformatted variable-length sequential file input failed at "
594                 "record #%jd (file offset %jd): record header has length %jd "
595                 "that does not match record footer (%jd)";
596       }
597     }
598   }
599   if (error) {
600     handler.SignalError(error, static_cast<std::intmax_t>(currentRecordNumber),
601         static_cast<std::intmax_t>(frameOffsetInFile_),
602         static_cast<std::intmax_t>(header), static_cast<std::intmax_t>(footer));
603     // TODO: error recovery
604   }
605   positionInRecord = sizeof header;
606 }
607 
608 void ExternalFileUnit::BeginSequentialVariableFormattedInputRecord(
609     IoErrorHandler &handler) {
610   if (this == defaultInput && defaultOutput) {
611     defaultOutput->FlushOutput(handler);
612   }
613   std::size_t length{0};
614   do {
615     std::size_t need{recordOffsetInFrame_ + length + 1};
616     length = ReadFrame(frameOffsetInFile_, need, handler);
617     if (length < need) {
618       handler.SignalEnd();
619       break;
620     }
621   } while (!SetSequentialVariableFormattedRecordLength());
622 }
623 
624 void ExternalFileUnit::BackspaceFixedRecord(IoErrorHandler &handler) {
625   RUNTIME_CHECK(handler, recordLength.has_value());
626   if (frameOffsetInFile_ < *recordLength) {
627     handler.SignalError(IostatBackspaceAtFirstRecord);
628   } else {
629     frameOffsetInFile_ -= *recordLength;
630   }
631 }
632 
633 void ExternalFileUnit::BackspaceVariableUnformattedRecord(
634     IoErrorHandler &handler) {
635   std::int32_t header{0}, footer{0};
636   auto headerBytes{static_cast<std::int64_t>(sizeof header)};
637   frameOffsetInFile_ += recordOffsetInFrame_;
638   recordOffsetInFrame_ = 0;
639   if (frameOffsetInFile_ <= headerBytes) {
640     handler.SignalError(IostatBackspaceAtFirstRecord);
641     return;
642   }
643   // Error conditions here cause crashes, not file format errors, because the
644   // validity of the file structure before the current record will have been
645   // checked informatively in NextSequentialVariableUnformattedInputRecord().
646   std::size_t got{
647       ReadFrame(frameOffsetInFile_ - headerBytes, headerBytes, handler)};
648   RUNTIME_CHECK(handler, got >= sizeof footer);
649   std::memcpy(&footer, Frame(), sizeof footer);
650   recordLength = footer;
651   RUNTIME_CHECK(handler, frameOffsetInFile_ >= *recordLength + 2 * headerBytes);
652   frameOffsetInFile_ -= *recordLength + 2 * headerBytes;
653   if (frameOffsetInFile_ >= headerBytes) {
654     frameOffsetInFile_ -= headerBytes;
655     recordOffsetInFrame_ = headerBytes;
656   }
657   auto need{static_cast<std::size_t>(
658       recordOffsetInFrame_ + sizeof header + *recordLength)};
659   got = ReadFrame(frameOffsetInFile_, need, handler);
660   RUNTIME_CHECK(handler, got >= need);
661   std::memcpy(&header, Frame() + recordOffsetInFrame_, sizeof header);
662   RUNTIME_CHECK(handler, header == *recordLength);
663 }
664 
665 // There's no portable memrchr(), unfortunately, and strrchr() would
666 // fail on a record with a NUL, so we have to do it the hard way.
667 static const char *FindLastNewline(const char *str, std::size_t length) {
668   for (const char *p{str + length}; p-- > str;) {
669     if (*p == '\n') {
670       return p;
671     }
672   }
673   return nullptr;
674 }
675 
676 void ExternalFileUnit::BackspaceVariableFormattedRecord(
677     IoErrorHandler &handler) {
678   // File offset of previous record's newline
679   auto prevNL{
680       frameOffsetInFile_ + static_cast<std::int64_t>(recordOffsetInFrame_) - 1};
681   if (prevNL < 0) {
682     handler.SignalError(IostatBackspaceAtFirstRecord);
683     return;
684   }
685   while (true) {
686     if (frameOffsetInFile_ < prevNL) {
687       if (const char *p{
688               FindLastNewline(Frame(), prevNL - 1 - frameOffsetInFile_)}) {
689         recordOffsetInFrame_ = p - Frame() + 1;
690         recordLength = prevNL - (frameOffsetInFile_ + recordOffsetInFrame_);
691         break;
692       }
693     }
694     if (frameOffsetInFile_ == 0) {
695       recordOffsetInFrame_ = 0;
696       recordLength = prevNL;
697       break;
698     }
699     frameOffsetInFile_ -= std::min<std::int64_t>(frameOffsetInFile_, 1024);
700     auto need{static_cast<std::size_t>(prevNL + 1 - frameOffsetInFile_)};
701     auto got{ReadFrame(frameOffsetInFile_, need, handler)};
702     RUNTIME_CHECK(handler, got >= need);
703   }
704   RUNTIME_CHECK(handler, Frame()[recordOffsetInFrame_ + *recordLength] == '\n');
705   if (*recordLength > 0 &&
706       Frame()[recordOffsetInFrame_ + *recordLength - 1] == '\r') {
707     --*recordLength;
708   }
709 }
710 
711 void ExternalFileUnit::DoImpliedEndfile(IoErrorHandler &handler) {
712   if (impliedEndfile_) {
713     impliedEndfile_ = false;
714     if (access == Access::Sequential && mayPosition()) {
715       DoEndfile(handler);
716     }
717   }
718 }
719 
720 void ExternalFileUnit::DoEndfile(IoErrorHandler &handler) {
721   endfileRecordNumber = currentRecordNumber;
722   Truncate(frameOffsetInFile_ + recordOffsetInFrame_, handler);
723   BeginRecord();
724   impliedEndfile_ = false;
725 }
726 
727 void ExternalFileUnit::CommitWrites() {
728   frameOffsetInFile_ +=
729       recordOffsetInFrame_ + recordLength.value_or(furthestPositionInRecord);
730   recordOffsetInFrame_ = 0;
731   BeginRecord();
732 }
733 
734 ChildIo &ExternalFileUnit::PushChildIo(IoStatementState &parent) {
735   OwningPtr<ChildIo> current{std::move(child_)};
736   Terminator &terminator{parent.GetIoErrorHandler()};
737   OwningPtr<ChildIo> next{New<ChildIo>{terminator}(parent, std::move(current))};
738   child_.reset(next.release());
739   return *child_;
740 }
741 
742 void ExternalFileUnit::PopChildIo(ChildIo &child) {
743   if (child_.get() != &child) {
744     child.parent().GetIoErrorHandler().Crash(
745         "ChildIo being popped is not top of stack");
746   }
747   child_.reset(child.AcquirePrevious().release()); // deletes top child
748 }
749 
750 void ChildIo::EndIoStatement() {
751   io_.reset();
752   u_.emplace<std::monostate>();
753 }
754 
755 bool ChildIo::CheckFormattingAndDirection(Terminator &terminator,
756     const char *what, bool unformatted, Direction direction) {
757   bool parentIsUnformatted{!parent_.get_if<FormattedIoStatementState>()};
758   bool parentIsInput{!parent_.get_if<IoDirectionState<Direction::Output>>()};
759   if (unformatted != parentIsUnformatted) {
760     terminator.Crash("Child %s attempted on %s parent I/O unit", what,
761         parentIsUnformatted ? "unformatted" : "formatted");
762     return false;
763   } else if (parentIsInput != (direction == Direction::Input)) {
764     terminator.Crash("Child %s attempted on %s parent I/O unit", what,
765         parentIsInput ? "input" : "output");
766     return false;
767   } else {
768     return true;
769   }
770 }
771 
772 } // namespace Fortran::runtime::io
773