Import getline helper from cdecl99.

[dxcommon.git] / src / getline.h

diff --git a/src/getline.h b/src/getline.h
new file mode 100644 (file)
index 0000000..b0f4999
--- /dev/null
+++ b/src/getline.h
@@ -0,0 +1,121 @@
+/*
+ * Copyright © 2024 Nick Bowler
+ *
+ * getline-like function which removes trailing newline (if any).
+ *
+ * If HAVE_GETLINE is not defined (or defined to 0) then a standard C
+ * implementation is used.  Othewrise, the POSIX getline function
+ * is called.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+#ifndef DX_GETLINE_H_
+#define DX_GETLINE_H_
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <limits.h>
+
+/*
+ * Size of the initial buffer allocated internally by the fallback
+ * implementation when *linebuf is NULL.
+ */
+#ifndef DX_GETLINE_INITIAL_ALLOC
+#  define DX_GETLINE_INITIAL_ALLOC 75
+#endif
+
+enum {
+       DX_GETLINE_OK     =  1,
+       DX_GETLINE_EOF    =  0,
+       DX_GETLINE_ERROR  = -1,
+       DX_GETLINE_ENOMEM = -2
+};
+
+/*
+ * Wrapper around getline with standard C fallback.
+ *
+ * Note that for portability to some getline implementations (e.g., FreeBSD)
+ * both *linebuf and *n should be set to zero on the initial call.
+ *
+ * If pre-allocating a buffer, ensure that its size is more than 1 byte,
+ * otherwise AIX 7.2 getline fails to work correctly.
+ *
+ * Returns 1 (DX_GETLINE_OK) if a line was read or 0 (DX_GETLINE_EOF) if
+ * no line could be read because the end of file was reached.
+ *
+ * On failure, returns a negative value.  If the C library input call failed
+ * then the return value is DX_GETLINE_ERROR and the reason for the failure
+ * should be available in errno.
+ *
+ * For the standard C fallback only, a return value of DX_GETLINE_ENOMEM
+ * indicates that the buffer allocation could not be expanded to fit the
+ * input line.
+ */
+static inline int dx_getline(char **linebuf, size_t *n, FILE *f)
+{
+#if HAVE_GETLINE
+       ssize_t rc;
+
+       if ((rc = getline(linebuf, n, f)) < 0) {
+               if (ferror(f))
+                       return DX_GETLINE_ERROR;
+               return DX_GETLINE_EOF;
+       }
+
+       if (rc-- && (*linebuf)[rc] == '\n')
+               (*linebuf)[rc] = '\0';
+
+       return DX_GETLINE_OK;
+#else
+       char *work = *linebuf;
+       size_t pos = 0;
+       size_t sz;
+
+       if (!work) {
+               sz = DX_GETLINE_INITIAL_ALLOC;
+               goto initial_alloc;
+       }
+
+       for (sz = *n;;) {
+               if (!fgets(&work[pos], sz - pos, f)) {
+                       if (ferror(f))
+                               return DX_GETLINE_ERROR;
+
+                       return pos ? DX_GETLINE_OK : DX_GETLINE_ERROR;
+               }
+
+               pos += strlen(&work[pos]);
+               if (work[pos-1] == '\n') {
+                       work[pos-1] = '\0';
+                       return DX_GETLINE_OK;
+               }
+
+               if (sz > INT_MAX/2 || sz > ((size_t)-1)/4)
+                       break;
+
+               sz = ((sz*4) + 2) / 3;
+initial_alloc:
+               work = realloc(work, sz);
+               if (!work)
+                       break;
+               *linebuf = work;
+               *n = sz;
+       }
+
+       return DX_GETLINE_ENOMEM;
+#endif
+}
+
+#endif