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 (Frame()[recordOffsetInFrame_ + *recordLength] == '\r') {
417           ++recordOffsetInFrame_;
418         }
419         if (Frame()[recordOffsetInFrame_ + *recordLength] == '\n') {
420           ++recordOffsetInFrame_;
421         }
422         recordOffsetInFrame_ += *recordLength;
423         recordLength.reset();
424       }
425     }
426   }
427   ++currentRecordNumber;
428   BeginRecord();
429 }
430 
431 bool ExternalFileUnit::AdvanceRecord(IoErrorHandler &handler) {
432   if (direction_ == Direction::Input) {
433     FinishReadingRecord(handler);
434     return BeginReadingRecord(handler);
435   } else { // Direction::Output
436     bool ok{true};
437     RUNTIME_CHECK(handler, isUnformatted.has_value());
438     if (isFixedRecordLength && recordLength) {
439       // Pad remainder of fixed length record
440       if (furthestPositionInRecord < *recordLength) {
441         WriteFrame(
442             frameOffsetInFile_, recordOffsetInFrame_ + *recordLength, handler);
443         std::memset(Frame() + recordOffsetInFrame_ + furthestPositionInRecord,
444             isUnformatted.value_or(false) ? 0 : ' ',
445             *recordLength - furthestPositionInRecord);
446       }
447     } else {
448       positionInRecord = furthestPositionInRecord;
449       if (isUnformatted.value_or(false)) {
450         // Append the length of a sequential unformatted variable-length record
451         // as its footer, then overwrite the reserved first four bytes of the
452         // record with its length as its header.  These four bytes were skipped
453         // over in BeginUnformattedIO<Output>().
454         // TODO: Break very large records up into subrecords with negative
455         // headers &/or footers
456         std::uint32_t length;
457         length = furthestPositionInRecord - sizeof length;
458         ok = ok &&
459             Emit(reinterpret_cast<const char *>(&length), sizeof length,
460                 sizeof length, handler);
461         positionInRecord = 0;
462         ok = ok &&
463             Emit(reinterpret_cast<const char *>(&length), sizeof length,
464                 sizeof length, handler);
465       } else {
466         // Terminate formatted variable length record
467         ok = ok && Emit("\n", 1, 1, handler); // TODO: Windows CR+LF
468       }
469     }
470     CommitWrites();
471     impliedEndfile_ = true;
472     ++currentRecordNumber;
473     return ok;
474   }
475 }
476 
477 void ExternalFileUnit::BackspaceRecord(IoErrorHandler &handler) {
478   if (access != Access::Sequential) {
479     handler.SignalError(IostatBackspaceNonSequential,
480         "BACKSPACE(UNIT=%d) on non-sequential file", unitNumber());
481   } else {
482     if (endfileRecordNumber && currentRecordNumber > *endfileRecordNumber) {
483       // BACKSPACE after ENDFILE
484     } else {
485       DoImpliedEndfile(handler);
486       if (frameOffsetInFile_ + recordOffsetInFrame_ > 0) {
487         --currentRecordNumber;
488         if (isFixedRecordLength) {
489           BackspaceFixedRecord(handler);
490         } else {
491           RUNTIME_CHECK(handler, isUnformatted.has_value());
492           if (isUnformatted.value_or(false)) {
493             BackspaceVariableUnformattedRecord(handler);
494           } else {
495             BackspaceVariableFormattedRecord(handler);
496           }
497         }
498       }
499     }
500     BeginRecord();
501   }
502 }
503 
504 void ExternalFileUnit::FlushOutput(IoErrorHandler &handler) {
505   if (!mayPosition()) {
506     auto frameAt{FrameAt()};
507     if (frameOffsetInFile_ >= frameAt &&
508         frameOffsetInFile_ <
509             static_cast<std::int64_t>(frameAt + FrameLength())) {
510       // A Flush() that's about to happen to a non-positionable file
511       // needs to advance frameOffsetInFile_ to prevent attempts at
512       // impossible seeks
513       CommitWrites();
514     }
515   }
516   Flush(handler);
517 }
518 
519 void ExternalFileUnit::FlushIfTerminal(IoErrorHandler &handler) {
520   if (isTerminal()) {
521     FlushOutput(handler);
522   }
523 }
524 
525 void ExternalFileUnit::Endfile(IoErrorHandler &handler) {
526   if (access != Access::Sequential) {
527     handler.SignalError(IostatEndfileNonSequential,
528         "ENDFILE(UNIT=%d) on non-sequential file", unitNumber());
529   } else if (!mayWrite()) {
530     handler.SignalError(IostatEndfileUnwritable,
531         "ENDFILE(UNIT=%d) on read-only file", unitNumber());
532   } else if (endfileRecordNumber &&
533       currentRecordNumber > *endfileRecordNumber) {
534     // ENDFILE after ENDFILE
535   } else {
536     DoEndfile(handler);
537     ++currentRecordNumber;
538   }
539 }
540 
541 void ExternalFileUnit::Rewind(IoErrorHandler &handler) {
542   if (access == Access::Direct) {
543     handler.SignalError(IostatRewindNonSequential,
544         "REWIND(UNIT=%d) on non-sequential file", unitNumber());
545   } else {
546     DoImpliedEndfile(handler);
547     SetPosition(0);
548     currentRecordNumber = 1;
549   }
550 }
551 
552 void ExternalFileUnit::EndIoStatement() {
553   io_.reset();
554   u_.emplace<std::monostate>();
555   lock_.Drop();
556 }
557 
558 void ExternalFileUnit::BeginSequentialVariableUnformattedInputRecord(
559     IoErrorHandler &handler) {
560   std::int32_t header{0}, footer{0};
561   std::size_t need{recordOffsetInFrame_ + sizeof header};
562   std::size_t got{ReadFrame(frameOffsetInFile_, need, handler)};
563   // Try to emit informative errors to help debug corrupted files.
564   const char *error{nullptr};
565   if (got < need) {
566     if (got == recordOffsetInFrame_) {
567       handler.SignalEnd();
568     } else {
569       error = "Unformatted variable-length sequential file input failed at "
570               "record #%jd (file offset %jd): truncated record header";
571     }
572   } else {
573     std::memcpy(&header, Frame() + recordOffsetInFrame_, sizeof header);
574     recordLength = sizeof header + header; // does not include footer
575     need = recordOffsetInFrame_ + *recordLength + sizeof footer;
576     got = ReadFrame(frameOffsetInFile_, need, handler);
577     if (got < need) {
578       error = "Unformatted variable-length sequential file input failed at "
579               "record #%jd (file offset %jd): hit EOF reading record with "
580               "length %jd bytes";
581     } else {
582       std::memcpy(&footer, Frame() + recordOffsetInFrame_ + *recordLength,
583           sizeof footer);
584       if (footer != header) {
585         error = "Unformatted variable-length sequential file input failed at "
586                 "record #%jd (file offset %jd): record header has length %jd "
587                 "that does not match record footer (%jd)";
588       }
589     }
590   }
591   if (error) {
592     handler.SignalError(error, static_cast<std::intmax_t>(currentRecordNumber),
593         static_cast<std::intmax_t>(frameOffsetInFile_),
594         static_cast<std::intmax_t>(header), static_cast<std::intmax_t>(footer));
595     // TODO: error recovery
596   }
597   positionInRecord = sizeof header;
598 }
599 
600 void ExternalFileUnit::BeginSequentialVariableFormattedInputRecord(
601     IoErrorHandler &handler) {
602   if (this == defaultInput && defaultOutput) {
603     defaultOutput->FlushOutput(handler);
604   }
605   std::size_t length{0};
606   do {
607     std::size_t need{recordOffsetInFrame_ + length + 1};
608     length = ReadFrame(frameOffsetInFile_, need, handler);
609     if (length < need) {
610       handler.SignalEnd();
611       break;
612     }
613   } while (!SetSequentialVariableFormattedRecordLength());
614 }
615 
616 void ExternalFileUnit::BackspaceFixedRecord(IoErrorHandler &handler) {
617   RUNTIME_CHECK(handler, recordLength.has_value());
618   if (frameOffsetInFile_ < *recordLength) {
619     handler.SignalError(IostatBackspaceAtFirstRecord);
620   } else {
621     frameOffsetInFile_ -= *recordLength;
622   }
623 }
624 
625 void ExternalFileUnit::BackspaceVariableUnformattedRecord(
626     IoErrorHandler &handler) {
627   std::int32_t header{0}, footer{0};
628   auto headerBytes{static_cast<std::int64_t>(sizeof header)};
629   frameOffsetInFile_ += recordOffsetInFrame_;
630   recordOffsetInFrame_ = 0;
631   if (frameOffsetInFile_ <= headerBytes) {
632     handler.SignalError(IostatBackspaceAtFirstRecord);
633     return;
634   }
635   // Error conditions here cause crashes, not file format errors, because the
636   // validity of the file structure before the current record will have been
637   // checked informatively in NextSequentialVariableUnformattedInputRecord().
638   std::size_t got{
639       ReadFrame(frameOffsetInFile_ - headerBytes, headerBytes, handler)};
640   RUNTIME_CHECK(handler, got >= sizeof footer);
641   std::memcpy(&footer, Frame(), sizeof footer);
642   recordLength = footer;
643   RUNTIME_CHECK(handler, frameOffsetInFile_ >= *recordLength + 2 * headerBytes);
644   frameOffsetInFile_ -= *recordLength + 2 * headerBytes;
645   if (frameOffsetInFile_ >= headerBytes) {
646     frameOffsetInFile_ -= headerBytes;
647     recordOffsetInFrame_ = headerBytes;
648   }
649   auto need{static_cast<std::size_t>(
650       recordOffsetInFrame_ + sizeof header + *recordLength)};
651   got = ReadFrame(frameOffsetInFile_, need, handler);
652   RUNTIME_CHECK(handler, got >= need);
653   std::memcpy(&header, Frame() + recordOffsetInFrame_, sizeof header);
654   RUNTIME_CHECK(handler, header == *recordLength);
655 }
656 
657 // There's no portable memrchr(), unfortunately, and strrchr() would
658 // fail on a record with a NUL, so we have to do it the hard way.
659 static const char *FindLastNewline(const char *str, std::size_t length) {
660   for (const char *p{str + length}; p-- > str;) {
661     if (*p == '\n') {
662       return p;
663     }
664   }
665   return nullptr;
666 }
667 
668 void ExternalFileUnit::BackspaceVariableFormattedRecord(
669     IoErrorHandler &handler) {
670   // File offset of previous record's newline
671   auto prevNL{
672       frameOffsetInFile_ + static_cast<std::int64_t>(recordOffsetInFrame_) - 1};
673   if (prevNL < 0) {
674     handler.SignalError(IostatBackspaceAtFirstRecord);
675     return;
676   }
677   while (true) {
678     if (frameOffsetInFile_ < prevNL) {
679       if (const char *p{
680               FindLastNewline(Frame(), prevNL - 1 - frameOffsetInFile_)}) {
681         recordOffsetInFrame_ = p - Frame() + 1;
682         *recordLength = prevNL - (frameOffsetInFile_ + recordOffsetInFrame_);
683         break;
684       }
685     }
686     if (frameOffsetInFile_ == 0) {
687       recordOffsetInFrame_ = 0;
688       *recordLength = prevNL;
689       break;
690     }
691     frameOffsetInFile_ -= std::min<std::int64_t>(frameOffsetInFile_, 1024);
692     auto need{static_cast<std::size_t>(prevNL + 1 - frameOffsetInFile_)};
693     auto got{ReadFrame(frameOffsetInFile_, need, handler)};
694     RUNTIME_CHECK(handler, got >= need);
695   }
696   RUNTIME_CHECK(handler, Frame()[recordOffsetInFrame_ + *recordLength] == '\n');
697   if (*recordLength > 0 &&
698       Frame()[recordOffsetInFrame_ + *recordLength - 1] == '\r') {
699     --*recordLength;
700   }
701 }
702 
703 void ExternalFileUnit::DoImpliedEndfile(IoErrorHandler &handler) {
704   if (impliedEndfile_) {
705     impliedEndfile_ = false;
706     if (access == Access::Sequential && mayPosition()) {
707       DoEndfile(handler);
708     }
709   }
710 }
711 
712 void ExternalFileUnit::DoEndfile(IoErrorHandler &handler) {
713   endfileRecordNumber = currentRecordNumber;
714   Truncate(frameOffsetInFile_ + recordOffsetInFrame_, handler);
715   BeginRecord();
716   impliedEndfile_ = false;
717 }
718 
719 void ExternalFileUnit::CommitWrites() {
720   frameOffsetInFile_ +=
721       recordOffsetInFrame_ + recordLength.value_or(furthestPositionInRecord);
722   recordOffsetInFrame_ = 0;
723   BeginRecord();
724 }
725 
726 ChildIo &ExternalFileUnit::PushChildIo(IoStatementState &parent) {
727   OwningPtr<ChildIo> current{std::move(child_)};
728   Terminator &terminator{parent.GetIoErrorHandler()};
729   OwningPtr<ChildIo> next{New<ChildIo>{terminator}(parent, std::move(current))};
730   child_.reset(next.release());
731   return *child_;
732 }
733 
734 void ExternalFileUnit::PopChildIo(ChildIo &child) {
735   if (child_.get() != &child) {
736     child.parent().GetIoErrorHandler().Crash(
737         "ChildIo being popped is not top of stack");
738   }
739   child_.reset(child.AcquirePrevious().release()); // deletes top child
740 }
741 
742 void ChildIo::EndIoStatement() {
743   io_.reset();
744   u_.emplace<std::monostate>();
745 }
746 
747 bool ChildIo::CheckFormattingAndDirection(Terminator &terminator,
748     const char *what, bool unformatted, Direction direction) {
749   bool parentIsUnformatted{!parent_.get_if<FormattedIoStatementState>()};
750   bool parentIsInput{!parent_.get_if<IoDirectionState<Direction::Output>>()};
751   if (unformatted != parentIsUnformatted) {
752     terminator.Crash("Child %s attempted on %s parent I/O unit", what,
753         parentIsUnformatted ? "unformatted" : "formatted");
754     return false;
755   } else if (parentIsInput != (direction == Direction::Input)) {
756     terminator.Crash("Child %s attempted on %s parent I/O unit", what,
757         parentIsInput ? "input" : "output");
758     return false;
759   } else {
760     return true;
761   }
762 }
763 
764 } // namespace Fortran::runtime::io
765