iterator based interface for file driven input [patch 11/14 from Nathanael]

.gitattributes

@@ -233,8 +233,16 @@ src/grid.c -text
 src/grid.h -text
 src/ieg.h -text
 src/ieglib.c -text
+src/input_file.c -text
+src/input_file.h -text
 src/institution.c -text
 src/institution.h -text
+src/iterator.c -text
+src/iterator.h -text
+src/iterator_fallback.c -text
+src/iterator_fallback.h -text
+src/iterator_grib.c -text
+src/iterator_grib.h -text
 src/make_cdilib -text
 src/make_fint.c -text
 src/mo_cdi.f90 -text
@@ -271,6 +279,8 @@ src/pkgconfig/cdi.pc.in -text
 src/pkgconfig/cdipio.pc.in -text
 src/proprietarySystemWorkarounds.c -text
 src/proprietarySystemWorkarounds.h -text
+src/referenceCounting.c -text
+src/referenceCounting.h -text
 src/resource_handle.c -text
 src/resource_handle.h -text
 src/resource_unpack.c -text

src/Makefile.am

@@ -56,8 +56,16 @@ libcdi_la_SOURCES = 	 \
 	grid.h	 	 \
 	ieg.h	 	 \
 	ieglib.c         \
+	input_file.c	\
+	input_file.h	\
 	institution.c  	 \
 	institution.h  	 \
+	iterator.c       \
+	iterator.h       \
+	iterator_fallback.c \
+	iterator_fallback.h \
+	iterator_grib.c \
+	iterator_grib.h  \
 	model.c        	 \
 	model.h        	 \
 	namespace.c      \
@@ -66,6 +74,8 @@ libcdi_la_SOURCES = 	 \
 	serialize.c	\
 	proprietarySystemWorkarounds.c \
 	proprietarySystemWorkarounds.h \
+	referenceCounting.c \
+	referenceCounting.h \
 	resource_handle.c\
 	resource_handle.h\
 	service.h	 \

src/Makefile.in

@@ -150,10 +150,10 @@ am_libcdi_la_OBJECTS = basetime.lo binary.lo calendar.lo cdf.lo \
 	cdf_int.lo cdi_error.lo cdi_util.lo cdiFortran.lo \
 	cgribexlib.lo dmemory.lo cksum.lo cdi_cksum.lo error.lo \
 	extralib.lo file.lo gaussgrid.lo gribapi.lo \
-	gribapi_utilities.lo grid.lo ieglib.lo \
-	institution.lo \
-	model.lo namespace.lo serialize.lo \
-	proprietarySystemWorkarounds.lo \
+	gribapi_utilities.lo grid.lo ieglib.lo input_file.lo \
+	institution.lo iterator.lo iterator_fallback.lo \
+	iterator_grib.lo model.lo namespace.lo serialize.lo \
+	proprietarySystemWorkarounds.lo referenceCounting.lo \
 	resource_handle.lo servicelib.lo stream_cdf.lo \
 	stream_cgribex.lo stream_ext.lo stream_grb.lo \
 	stream_gribapi.lo stream_history.lo stream_ieg.lo \
@@ -488,8 +488,16 @@ libcdi_la_SOURCES = \
 	grid.h	 	 \
 	ieg.h	 	 \
 	ieglib.c         \
+	input_file.c	 \
+	input_file.h	 \
 	institution.c  	 \
 	institution.h  	 \
+	iterator.c       \
+	iterator.h       \
+	iterator_fallback.c \
+	iterator_fallback.h \
+	iterator_grib.c \
+	iterator_grib.h  \
 	model.c        	 \
 	model.h        	 \
 	namespace.c      \
@@ -498,6 +506,8 @@ libcdi_la_SOURCES = \
 	serialize.c	\
 	proprietarySystemWorkarounds.c \
 	proprietarySystemWorkarounds.h \
+	referenceCounting.c\
+	referenceCounting.h\
 	resource_handle.c\
 	resource_handle.h\
 	service.h	 \
@@ -731,7 +741,11 @@ distclean-compile:
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/gribapi_utilities.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/grid.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/ieglib.Plo@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/input_file.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/institution.Plo@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/iterator.Plo@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/iterator_fallback.Plo@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/iterator_grib.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/model.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/namespace.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/pio.Plo@am__quote@
@@ -750,6 +764,7 @@ distclean-compile:
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/pio_server.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/pio_util.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/proprietarySystemWorkarounds.Plo@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/referenceCounting.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/resource_handle.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/resource_unpack.Plo@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/serialize.Plo@am__quote@

src/cdi.h

@@ -31,6 +31,7 @@ extern "C" {
 /* Error identifier */
 
 #define	 CDI_NOERR        	  0   /* No Error                             */
+#define  CDI_EEOF                -1   /* The end of file was encountered      */
 #define  CDI_ESYSTEM            -10   /* Operating system error               */
 #define  CDI_EINVAL             -20   /* Invalid argument                     */
 #define  CDI_EUFTYPE            -21   /* Unsupported file type                */
@@ -222,6 +223,17 @@ extern "C" {
 /* number of unsigned char needed to store UUID */
 #define  CDI_UUID_SIZE           16
 
+/* Structs that are used to return data to the user */
+
+typedef struct CdiParam { int discipline, category, number; } CdiParam;
+
+
+/* Opaque types */
+
+typedef struct CdiIterator CdiIterator;
+typedef struct CdiGribIterator CdiGribIterator;
+
+
 /* CDI control routines */
 
 void    cdiReset(void);
@@ -358,6 +370,62 @@ void    streamCopyRecord(int streamIDdest, int streamIDsrc);
 
 void    streamInqGRIBinfo(int streamID, int *intnum, float *fltnum, off_t *bignum);
 
+
+/* File driven I/O (may yield better performance than using the streamXXX functions) */
+
+//Creation & Destruction
+CdiIterator* cdiIterator_new(const char* path);  //Requires a subsequent call to cdiIteratorNextField() to point the iterator at the first field.
+CdiIterator* cdiIterator_clone(CdiIterator* me);
+char* cdiIterator_serialize(CdiIterator* me);  //Returns a malloc'ed string.
+CdiIterator* cdiIterator_deserialize(const char* description);  //description is a string that was returned by cdiIteratorSerialize(). Returns a copy of the original iterator.
+void cdiIterator_print(CdiIterator* me, FILE* stream);
+void cdiIterator_delete(CdiIterator* me);
+
+//Advancing an iterator
+int cdiIterator_nextField(CdiIterator* me);      //Points the iterator at the next field, returns CDI_EEOF if there are no more fields in the file.
+
+//Introspecting metadata
+//All outXXX arguments to these functions may be NULL.
+char* cdiIterator_inqStartTime(CdiIterator* me);      //Returns the (start) time as an ISO-8601 coded string. The caller is responsible to free() the returned string.
+char* cdiIterator_inqEndTime(CdiIterator* me);      //Returns the end time of an integration period as an ISO-8601 coded string, or NULL if there is no end time. The caller is responsible to free() the returned string.
+char* cdiIterator_inqVTime(CdiIterator* me);      //Returns the validity date as an ISO-8601 coded string. The caller is responsible to free() the returned string.
+int cdiIterator_inqLevelType(CdiIterator* me, int levelSelector, char** outName, char** outLongName, char** outStdName, char** outUnit);      //callers are responsible to free() strings that they request
+int cdiIterator_inqLevel(CdiIterator* me, int levelSelector, double* outValue1, double* outValue2);       //outValue2 is only written to if the level is a hybrid level
+int cdiIterator_inqLevelUuid(CdiIterator* me, int* outVgridNumber, int* outLevelCount, unsigned char (*outUuid)[CDI_UUID_SIZE]);   //outUuid must point to a buffer of 16 bytes, returns an error code if no generalized zaxis is used.
+CdiParam cdiIterator_inqParam(CdiIterator* me);
+int cdiIterator_inqDatatype(CdiIterator* me);
+int cdiIterator_inqTsteptype(CdiIterator* me);
+char* cdiIterator_inqVariableName(CdiIterator* me);        //The caller is responsible to free() the returned buffer.
+int cdiIterator_inqGridId(CdiIterator* me);         //The returned id is only valid until the next call to cdiIteratorNextField().
+
+//Reading data
+void cdiIterator_readField(CdiIterator* me, double* data_vec, size_t* nmiss);
+void cdiIterator_readFieldF(CdiIterator* me, float* data_vec, size_t* nmiss);
+//TODO[NH]: Add functions to read partial fields.
+
+
+//Direct access to grib fields
+CdiGribIterator* cdiGribIterator_clone(CdiIterator* me);  //Returns NULL if the associated file is not a GRIB file.
+void cdiGribIterator_delete(CdiGribIterator* me);
+
+//Callthroughs to GRIB-API
+int cdiGribIterator_getLong(CdiGribIterator* me, const char* key, long* value); //Same semantics as grib_get_long().
+int cdiGribIterator_getDouble(CdiGribIterator* me, const char* key, double* value); //Same semantics as grib_get_double().
+int cdiGribIterator_getLength(CdiGribIterator* me, const char* key, size_t* value);     //Same semantics as grib_get_length().
+int cdiGribIterator_getString(CdiGribIterator* me, const char* key, char* value, size_t* length);       //Same semantics as grib_get_string().
+int cdiGribIterator_getSize(CdiGribIterator* me, const char* key, size_t* value);     //Same semantics as grib_get_size().
+int cdiGribIterator_getLongArray(CdiGribIterator* me, const char* key, long* value, size_t* array_size);       //Same semantics as grib_get_long_array().
+int cdiGribIterator_getDoubleArray(CdiGribIterator* me, const char* key, double* value, size_t* array_size);       //Same semantics as grib_get_double_array().
+
+//Convenience functions for accessing GRIB-API keys
+int cdiGribIterator_inqEdition(CdiGribIterator* me);
+long cdiGribIterator_inqLongValue(CdiGribIterator* me, const char* key);   //Aborts on failure to fetch the given key.
+long cdiGribIterator_inqLongDefaultValue(CdiGribIterator* me, const char* key, long defaultValue); //Returns the default value if the given key is not present.
+double cdiGribIterator_inqDoubleValue(CdiGribIterator* me, const char* key);   //Aborts on failure to fetch the given key.
+double cdiGribIterator_inqDoubleDefaultValue(CdiGribIterator* me, const char* key, double defaultValue); //Returns the default value if the given key is not present.
+char* cdiGribIterator_inqStringValue(CdiGribIterator* me, const char* key);        //Returns a malloc'ed string.
+
+
 /* VLIST routines */
 
 /*      vlistCreate: Create a variable list */

src/cdi.inc

@@ -31,6 +31,8 @@
 !
       INTEGER    CDI_NOERR             
       PARAMETER (CDI_NOERR              =  0)
+      INTEGER    CDI_EEOF              
+      PARAMETER (CDI_EEOF               = -1)
       INTEGER    CDI_ESYSTEM           
       PARAMETER (CDI_ESYSTEM            = -10)
       INTEGER    CDI_EINVAL            
@@ -377,6 +379,12 @@
       INTEGER    CDI_UUID_SIZE         
       PARAMETER (CDI_UUID_SIZE          = 16)
 !
+!  Structs that are used to return data to the user
+!
+!
+!  Opaque types
+!
+!
 !  CDI control routines
 !
 !                     cdiReset
@@ -691,6 +699,9 @@
 !                                     INTEGER         streamIDsrc)
       EXTERNAL        streamCopyRecord
 
+!
+!  File driven I/O (may yield better performance than using the streamXXX functions)
+!
 !
 !  VLIST routines
 !
@@ -1958,6 +1969,15 @@
 !                                    (INTEGER         zaxisID)
       EXTERNAL        zaxisInqLtype
 
+!                     zaxisDefLtype2
+!                                    (INTEGER         zaxisID,
+!                                     INTEGER         ltype)
+      EXTERNAL        zaxisDefLtype2
+
+      INTEGER         zaxisInqLtype2
+!                                    (INTEGER         zaxisID)
+      EXTERNAL        zaxisInqLtype2
+
 !                     zaxisDefVct
 !                                    (INTEGER         zaxisID,
 !                                     INTEGER         size,

src/cdiFortran.c

@@ -60,6 +60,12 @@
 /*  number of unsigned char needed to store UUID  */
 
 
+/*  Structs that are used to return data to the user  */
+
+
+/*  Opaque types  */
+
+
 /*  CDI control routines  */
 
 FCALLSCSUB0 (cdiReset, CDIRESET, cdireset)
@@ -143,6 +149,9 @@ FCALLSCSUB3 (streamWriteRecordF, STREAMWRITERECORDF, streamwriterecordf, INT, PF
 FCALLSCSUB3 (streamReadRecord, STREAMREADRECORD, streamreadrecord, INT, PDOUBLE, PINT)
 FCALLSCSUB2 (streamCopyRecord, STREAMCOPYRECORD, streamcopyrecord, INT, INT)
 
+/*  File driven I/O (may yield better performance than using the streamXXX functions)  */
+
+
 /*  VLIST routines  */
 
 FCALLSCFUN0 (INT, vlistCreate, VLISTCREATE, vlistcreate)
@@ -412,6 +421,8 @@ FCALLSCSUB2 (zaxisDefPositive, ZAXISDEFPOSITIVE, zaxisdefpositive, INT, INT)
 FCALLSCFUN1 (INT, zaxisInqPositive, ZAXISINQPOSITIVE, zaxisinqpositive, INT)
 FCALLSCSUB2 (zaxisDefLtype, ZAXISDEFLTYPE, zaxisdefltype, INT, INT)
 FCALLSCFUN1 (INT, zaxisInqLtype, ZAXISINQLTYPE, zaxisinqltype, INT)
+FCALLSCSUB2 (zaxisDefLtype2, ZAXISDEFLTYPE2, zaxisdefltype2, INT, INT)
+FCALLSCFUN1 (INT, zaxisInqLtype2, ZAXISINQLTYPE2, zaxisinqltype2, INT)
 FCALLSCSUB3 (zaxisDefVct, ZAXISDEFVCT, zaxisdefvct, INT, INT, PDOUBLE)
 FCALLSCSUB2 (zaxisInqVct, ZAXISINQVCT, zaxisinqvct, INT, PDOUBLE)
 FCALLSCFUN1 (INT, zaxisInqVctSize, ZAXISINQVCTSIZE, zaxisinqvctsize, INT)

src/input_file.c

+#include "input_file.h"
+
+#include "cdi.h"
+#include "dmemory.h"
+#include "proprietarySystemWorkarounds.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <pthread.h>
+#include <string.h>
+#include <unistd.h>
+
+static void cdiInputFile_destruct(CdiInputFile* me);
+
+//For an explanation of the condestruct() pattern, see the comment in iterator_grib.c
+//path != NULL -> construction
+//path = NULL -> destruction
+static CdiInputFile* condestruct(CdiInputFile* me, const char* path)
+{
+  #define super() (&me->super)
+  if(!path) goto destruct;
+  cdiRefObject_construct(super());
+  me->path = myStrDup(path);
+  if(!me->path) goto destructSuper;
+  do
+    {
+      me->fileDescriptor = open(me->path, O_RDONLY);
+    }
+  while(me->fileDescriptor == -1 && (errno == EINTR || errno == EAGAIN));
+  if(me->fileDescriptor == -1) goto freePath;
+  //construction successfull, now we can set our own destructor
+  super()->destructor = (void(*)(CdiReferencedObject*))cdiInputFile_destruct;
+  goto success;
+
+// ^        constructor code       ^
+// |                               |
+// v destructor/error-cleanup code v
+
+destruct:
+  close(me->fileDescriptor);
+freePath:
+  free(me->path);
+destructSuper:
+  cdiRefObject_destruct(super());
+  me = NULL;
+
+success:
+  return me;
+  #undef super
+}
+
+static CdiInputFile** openFileList = NULL;
+static size_t openFileCount = 0, openFileListSize = 0;
+static pthread_mutex_t openFileListLock = PTHREAD_MUTEX_INITIALIZER;
+
+//This either returns a new object, or retains and returns a preexisting open file.
+CdiInputFile* cdiInputFile_make(const char* path)
+{
+  CdiInputFile* result = NULL;
+  xassert(path);
+  int error = pthread_mutex_lock(&openFileListLock);
+  xassert(!error);
+    {
+      //Check the list of open files for the given path.
+      for(size_t i = openFileCount; i-- && !result; )
+        {
+          if(!strcmp(path, openFileList[i]->path)) result = openFileList[i];
+        }
+      //If no open file was found, we open one, otherwise we just retain the existing one one more time.
+      if(result)
+        {
+          cdiRefObject_retain(&result->super);
+        }
+      else
+        {
+          result = xmalloc(sizeof(*result));
+          if(!condestruct(result, path))
+            {
+              //An error occured during construction, avoid a memory leak.
+              free(result);
+              result = NULL;
+            }
+          else
+            {
+              //Add the new file to the list of open files.
+              if(openFileCount == openFileListSize)
+                {
+                  openFileListSize *= 2;
+                  if(openFileListSize < 16) openFileListSize = 16;
+                  openFileList = xrealloc(openFileList, openFileListSize);
+                }
+              xassert(openFileCount < openFileListSize);
+              openFileList[openFileCount++] = result;
+            }
+        }
+    }
+  error = pthread_mutex_unlock(&openFileListLock);
+  xassert(!error);
+  return result;
+}
+
+int cdiInputFile_read(const CdiInputFile* me, off_t readPosition, size_t readSize, size_t* outActualReadSize, void* buffer)
+{
+  char* byteBuffer = buffer;
+  size_t trash;
+  if(!outActualReadSize) outActualReadSize = &trash;
+  *outActualReadSize = 0;
+  while(readSize)
+    {
+      ssize_t bytesRead = pread(me->fileDescriptor, byteBuffer, readSize, readPosition);
+      if(bytesRead == -1) return (errno == EINVAL) ?  CDI_EINVAL : CDI_ESYSTEM;
+      if(bytesRead == 0) return CDI_EEOF;
+      byteBuffer += bytesRead;
+      readPosition += bytesRead;
+      readSize -= bytesRead;
+      *outActualReadSize += bytesRead;
+    }
+  return CDI_NOERR;
+}
+
+char* cdiInputFile_copyPath(const CdiInputFile* me)
+{
+  return myStrDup(me->path);
+}
+
+void cdiInputFile_destruct(CdiInputFile* me)
+{
+  int error = pthread_mutex_lock(&openFileListLock);
+  xassert(!error);
+    {
+      //Find the position of me in the list of open files.
+      ssize_t position;
+      for(position = openFileCount; position--; ) if(openFileList[position] == me) break;
+      xassert(position != -1);
+      //Remove me from the list
+      openFileList[position] = openFileList[--openFileCount];
+    }
+  error = pthread_mutex_unlock(&openFileListLock);
+  xassert(!error);
+  condestruct(me, NULL);
+}

src/input_file.h

+#ifndef INCLUDE_GUARD_CDI_GRIB_FILE_H
+#define INCLUDE_GUARD_CDI_GRIB_FILE_H
+
+#include "referenceCounting.h"
+
+/*
+CdiInputFile is a file abstraction that allows accessing an input file through any number of channels:
+It is reference counted, so that it is closed at the right place,
+and it is stateless, so that accesses from different callers cannot interfere with each other.
+Once the reference counting code is threadsafe, CdiInputFile will also be threadsafe.
+*/
+typedef struct CdiInputFile {
+  //public:
+    CdiReferencedObject super;
+
+  //private:
+    char* path;
+    int fileDescriptor;
+} CdiInputFile;
+
+//Final class, the constructor is private and not defined here.
+CdiInputFile* cdiInputFile_make(const char* path);   //The caller is responsible to call cdiRefObject_release() on the returned object.
+int cdiInputFile_read(const CdiInputFile* me, off_t readPosition, size_t readSize, size_t* outActualReadSize, void* buffer);       //Returns one of CDI_EINVAL, CDI_ESYSTEM, CDI_EEOF, OR CDI_NOERR.
+char* cdiInputFile_copyPath(const CdiInputFile* me);    //Returns a malloc'ed string, don't forget to free() it.
+//Destructor is private as well.
+
+#endif

src/iterator.h

+/*
+ * This file is for the use of iterator.c and the CdiIterator subclasses only.
+ */
+
+#ifndef INCLUDE_GUARD_CDI_ITERATOR_INT_H
+#define INCLUDE_GUARD_CDI_ITERATOR_INT_H
+
+#include "cdi.h"
+
+#include <stdbool.h>
+
+/*
+class CdiIterator
+
+An iterator is an object that identifies the position of one record in a file, where a record is defined as the data belonging to one level, timestep, and variable.
+Using iterators to read a file can be significantly faster than using streams, because they can avoid building an index of the file.
+For file formats like grib that do not provide an index within the file, this makes the difference between reading the file once or reading the file twice.
+
+CdiIterator is an abstract base class. Which derived class is used depends on the type of the file. The class hierarchy currently looks like this:
+
+    CdiIterator <|--+-- CdiFallbackIterator
+                    |
+                    +-- CdiGribIterator
+
+The fallback implementation currently uses the stream interface of CDI under the hood to provide full functionality for all filetypes for which no iterator implementation exists yet.
+*/
+//TODO[NH]: Debug messages, print function.
+
+struct CdiIterator {
+  int filetype;      //This is used to dispatch calls to the correct subclass.
+  bool isAdvanced;    //Used to catch inquiries before the first call to CdiIteratorNextField(). //XXX: Advanced is probably not a good word (initialized?)
+
+  //The metadata that can be accessed by the inquiry calls.
+  //While theoretically redundant, these fields allow the handling of most inquiry calls within the base class.
+  //Only the name is excempted because it needs an allocation.
+  //These fields are set by the subclasses in the xxxIterNextField() method.
+  int datatype, timesteptype;
+  int gridId;
+  CdiParam param;
+
+  //The status information for reading/advancing is added in the subclasses.
+};
+
+void baseIterConstruct(CdiIterator* me, int filetype);
+const char* baseIter_constructFromString(CdiIterator* me, const char* description);     //Returns a pointer past the end of the parsed portion of the description string.
+void baseIterDestruct(CdiIterator* me);
+
+#endif

src/iterator_fallback.c

+#include "iterator_fallback.h"
+
+#include "cdi.h"
+#include "cdi_int.h"
+#include "dmemory.h"
+#include "proprietarySystemWorkarounds.h"
+#include "vlist.h"      //Required for vlist_t, which we require because there is no safe function available to access a variable name.
+
+#include <assert.h>
+#include <stdlib.h>
+
+//For more information on the condestruct() pattern, see comment in src/iterator_grib.c
+static CdiFallbackIterator* condestruct(CdiFallbackIterator* me, const char* path, int filetype)
+{
+  if(me) goto destruct;
+
+  me = xmalloc(sizeof(*me));
+  baseIterConstruct(&me->super, filetype);
+
+  me->streamId = streamOpenRead(path);
+  if(me->streamId == CDI_UNDEFID) goto destructSuper;
+  me->vlistId = streamInqVlist(me->streamId);
+  if(me->vlistId == CDI_UNDEFID) goto closeStream;
+  me->variableCount = vlistNvars(me->vlistId);
+  if(me->variableCount <= 0) goto closeStream;
+  me->curLevelCount = -1;        //Will be set in cdiFallbackIterator_nextField()
+
+  //These values are chosen so that the natural increment at the start of cdiFallbackIterator_nextField() will correctly position us at the first slice.
+  me->curTimestep = 0;
+  if(streamInqTimestep(me->streamId, me->curTimestep) <= 0) goto closeStream;
+  me->curVariable = 0;
+  me->curLevel = -1;
+  me->path = myStrDup(path);
+  if(!me->path) goto closeStream;
+
+  return me;
+
+// ^        constructor code        ^
+// |                                |
+// v destructor/error-cleanup code  v
+
+destruct:
+  free(me->path);
+closeStream:
+  streamClose(me->streamId);
+destructSuper:
+  baseIterDestruct(&me->super);
+  free(me);
+  return NULL;
+}
+
+CdiIterator* cdiFallbackIterator_new(const char* path, int filetype)
+{
+  return &condestruct(NULL, path, filetype)->super;
+}
+
+//Fetches the info that is published by the variables in the base class from the current field.
+static void fetchSuperInfo(CdiFallbackIterator* me)
+{
+  me->super.datatype = vlistInqVarDatatype(me->vlistId, me->curVariable);
+  me->super.timesteptype = vlistInqVarTsteptype(me->vlistId, me->curVariable);
+  me->super.gridId = vlistInqVarGrid(me->vlistId, me->curVariable);
+  int param = vlistInqVarParam(me->vlistId, me->curVariable);
+  cdiDecodeParam(param, &me->super.param.number, &me->super.param.category, &me->super.param.discipline);
+}
+
+CdiFallbackIterator* cdiFallbackIterator_clone(CdiIterator* super)
+{
+  CdiFallbackIterator* me = (CdiFallbackIterator*)super;
+
+  //Make another stream for this file. This yields an unadvanced iterator.
+  CdiFallbackIterator* clone = condestruct(NULL, me->path, me->super.filetype);
+  if(!clone) return NULL;
+
+  //Point the clone to the same position in the file.
+  clone->variableCount = me->variableCount;
+  clone->curVariable = me->curVariable;
+  clone->curLevelCount = me->curLevelCount;
+  clone->curLevel = me->curLevel;
+  clone->curTimestep = me->curTimestep;
+
+  clone->super.isAdvanced = super->isAdvanced;
+  if(super->isAdvanced) fetchSuperInfo(clone);
+
+  return clone;
+}
+
+char* cdiFallbackIterator_serialize(CdiIterator* super)
+{
+  CdiFallbackIterator* me = (CdiFallbackIterator*)super;
+
+  char* escapedPath = cdiEscapeSpaces(me->path);
+  char* result = myAsprintf("%s %d %d %d %d %d", escapedPath, me->variableCount, me->curVariable, me->curLevelCount, me->curLevel, me->curTimestep);
+  free(escapedPath);
+  return result;
+}
+
+CdiFallbackIterator* cdiFallbackIterator_deserialize(const char* description)
+{
+  CdiFallbackIterator* me = xmalloc(sizeof(*me));
+  if(!me) goto fail;
+
+  description = baseIter_constructFromString(&me->super, description);
+
+  while(*description == ' ') description++;
+  me->path = cdiUnescapeSpaces(description, &description);
+  if(!me->path) goto destructSuper;
+
+  me->streamId = streamOpenRead(me->path);
+  if(me->streamId == CDI_UNDEFID) goto freePath;
+  me->vlistId = streamInqVlist(me->streamId);
+  if(me->vlistId == CDI_UNDEFID) goto closeStream;
+
+  //This reads one variable from the description string, does error checking, and advances the given string pointer.
+  #define decodeValue(variable, description) do \
+    { \
+      const char* savedStart = description; \
+      long long decodedValue = strtoll(description, (char**)&description, 0);   /*The cast is a workaround for the wrong signature of strtoll().*/ \
+      variable = (int)decodedValue; \
+      if(savedStart == description) goto closeStream; \
+      if((long long)decodedValue != (long long)variable) goto closeStream; \
+    } while(0)
+  decodeValue(me->variableCount, description);