impr: fileio - add offset and limit (nalgeon#68)

oranav · Feb 22, 2023 · db539b0 · db539b0
1 parent 07549eb
commit db539b0
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Showing 2 changed files with 47 additions and 7 deletions.
diff --git a/docs/fileio.md b/docs/fileio.md
@@ -12,9 +12,11 @@ Main features:
 -   Create a symlink.
 -   List files in a directory.
 
-### fileio_read(path)
+### fileio_read(path [,offset [,limit]])
 
 Reads the file specified by `path` and returns its contents as `blob`.
+If offset is supplied and is non-zero and less than the file size, then seek to that offset before reading.
+If limit is supplied and is non-zero then limit the number of bytes read to limit.
 
 ```sql
 select fileio_write('hello.txt', 'hello world');

diff --git a/src/fileio/legacy.c b/src/fileio/legacy.c
@@ -83,7 +83,7 @@ SQLITE_EXTENSION_INIT3
 ** Throw an SQLITE_IOERR if there are difficulties pulling the file
 ** off of disk.
 */
-static void readFileContents(sqlite3_context* ctx, const char* zName) {
+static void readFileContents(sqlite3_context* ctx, const char* zName, const int nOffset, const int nLimit) {
     FILE* in;
     sqlite3_int64 nIn;
     void* pBuf;
@@ -98,6 +98,23 @@ static void readFileContents(sqlite3_context* ctx, const char* zName) {
     fseek(in, 0, SEEK_END);
     nIn = ftell(in);
     rewind(in);
+    if (nOffset > nIn) { /* offset is greater than the size of the file */
+        sqlite3_result_error_code(ctx, SQLITE_TOOBIG);
+        fclose(in);
+        return;
+    }
+    if (nLimit <0){
+        sqlite3_result_error_code(ctx, SQLITE_TOOBIG);
+        fclose(in);
+        return;
+    }
+    if (nOffset > 0) {
+        fseek(in, nOffset, SEEK_SET);
+	nIn -= nOffset;
+    }
+    if (nLimit>0 && nLimit < nIn){
+        nIn=nLimit;
+    }
     db = sqlite3_context_db_handle(ctx);
     mxBlob = sqlite3_limit(db, SQLITE_LIMIT_LENGTH, -1);
     if (nIn > mxBlob) {
@@ -127,11 +144,32 @@ static void readFileContents(sqlite3_context* ctx, const char* zName) {
 */
 static void sqlite3_readfile(sqlite3_context* context, int argc, sqlite3_value** argv) {
     const char* zName;
-    (void)(argc); /* Unused parameter */
+    int nOffset;
+    int nLimit;
     zName = (const char*)sqlite3_value_text(argv[0]);
     if (zName == 0)
         return;
-    readFileContents(context, zName);
+    nOffset=0;
+    nLimit=0;
+
+    if (argc>=2 && sqlite3_value_type(argv[1])!=SQLITE_NULL) {
+        nOffset=sqlite3_value_int(argv[1]);
+        if (nOffset<0) {
+            sqlite3_result_error(context, "offset must be >= 0", -1);
+            return;
+        }
+    }
+
+    if (argc==3 && sqlite3_value_type(argv[2])!=SQLITE_NULL) {
+        nLimit=sqlite3_value_int(argv[2]);
+        if (nLimit<0) {
+            sqlite3_result_error(context, "limit must be >= 0", -1);
+            return;
+        }
+    }
+
+
+    readFileContents(context, zName, nOffset, nLimit);
 }
 
 /*
@@ -967,8 +1005,8 @@ int fileio_scalar_init(sqlite3* db) {
     sqlite3_create_function(db, "fileio_mkdir", -1, flags, 0, sqlite3_mkdir, 0, 0);
     sqlite3_create_function(db, "mkdir", -1, flags, 0, sqlite3_mkdir, 0, 0);
 
-    sqlite3_create_function(db, "fileio_read", 1, flags, 0, sqlite3_readfile, 0, 0);
-    sqlite3_create_function(db, "readfile", 1, flags, 0, sqlite3_readfile, 0, 0);
+    sqlite3_create_function(db, "fileio_read", -1, flags, 0, sqlite3_readfile, 0, 0);
+    sqlite3_create_function(db, "readfile", -1, flags, 0, sqlite3_readfile, 0, 0);
 
     sqlite3_create_function(db, "fileio_symlink", 2, flags, 0, sqlite3_symlink, 0, 0);
     sqlite3_create_function(db, "symlink", 2, flags, 0, sqlite3_symlink, 0, 0);
@@ -1153,4 +1191,4 @@ INT closedir(LPDIR dirp) {
     sqlite3_free(dirp);
     return result;
 }
-#endif
+#endif