2 files changed, 117 insertions, 0 deletions
diff --git a/src/io/lines.c b/src/io/lines.c
new file mode 100644
index 0000000..6367c1d
--- /dev/null
+++ b/src/io/lines.c
@@ -0,0 +1,92 @@
+#include <stdlib.h>
+#include <string.h>
+
+#include "lines.h"
+#include "util/debug.h"
+#include "util/error.h"
+
+
+bool file_lines_open(const char *progname, const char *fname, FILE *f, struct file_lines *dst) {
+  dst->f = f;
+
+  dst->cap = 4096;
+  dst->buffer = malloc(dst->cap);
+  if (!dst->buffer) {
+    print_error_nomem(progname);
+    return false;
+  }
+
+  dst->cursor = 0;
+  dst->readfrom = (size_t)-1;
+  dst->progname = progname;
+  dst->fname = fname;
+  return true;
+}
+
+bool file_lines_read(struct file_lines *fl, struct string_view *dst) {
+  // Return already-read line if we have any
+  if (fl->readfrom != (size_t)-1) {
+    char *p = memchr(fl->buffer + fl->readfrom, '\n', fl->cursor - fl->readfrom);
+    if (p != NULL) {
+      dst->s = fl->buffer + fl->readfrom;
+      dst->len = p - (fl->buffer + fl->readfrom);
+      fl->readfrom = p - fl->buffer + 1;
+      DEBUG("next line from %zu len %zu\n", fl->readfrom, dst->len);
+      return true;
+    }
+
+    DEBUG("no more newlines, moving back from %zu len %zu\n", fl->readfrom, fl->cursor - fl->readfrom);
+    // move back whatever we have left
+    memmove(fl->buffer, fl->buffer + fl->readfrom, fl->cursor - fl->readfrom);
+    fl->cursor -= fl->readfrom;
+  }
+
+  DEBUG("cursor=%zu\n", fl->cursor);
+
+  // read a line
+  size_t linelen = 0;
+  while (true) {
+    // grow buffer when small
+    if (fl->cap - fl->cursor < 1024) {
+      fl->cap *= 2;
+      if (fl->cap == 0) {
+        fprintf(stderr, "%s: Regel te lang\n", fl->progname);
+        exit(1);
+      }
+      DEBUG("realloc to cap %zu\n", fl->cap);
+      fl->buffer = realloc(fl->buffer, fl->cap);
+      if (!fl->buffer) print_error_nomem(fl->progname);
+    }
+
+    size_t nr = fread(fl->buffer + fl->cursor, 1, fl->cap - fl->cursor, fl->f);
+    DEBUG("nr=%zu\n", nr);
+    if (nr == 0) {
+      if (feof(fl->f)) {
+        if (fl->cursor == 0) return false;
+        linelen = fl->cursor;
+        break;
+      }
+      if (fl->fname) fprintf(stderr, "%s: Fout bij lezen van bestand '%s'\n", fl->progname, fl->fname);
+      else fprintf(stderr, "%s: Fout bij lezen van standaardinvoer\n", fl->progname);
+      exit(1);
+    }
+    char *p = memchr(fl->buffer + fl->cursor, '\n', nr);
+    fl->cursor += nr;
+    if (p != NULL) {
+      linelen = p - fl->buffer;
+      break;
+    }
+  }
+
+  DEBUG("line with len %zu (cursor=%zu)\n", linelen, fl->cursor);
+
+  // we have a newline at buffer + linelen; return lines in buffer
+  dst->s = fl->buffer;
+  dst->len = linelen;
+  fl->readfrom = linelen + 1;
+  return true;
+}
+
+void file_lines_close(struct file_lines *fl) {
+  free(fl->buffer);
+}
diff --git a/src/io/lines.h b/src/io/lines.h
new file mode 100644
index 0000000..b09b756
--- /dev/null
+++ b/src/io/lines.h
@@ -0,0 +1,25 @@
+#pragma once
+
+#include <stdio.h>
+#include <stdbool.h>
+
+#include "util/string_view.h"
+
+
+struct file_lines {
+  const char *progname, *fname;
+
+  FILE *f;
+  size_t cap;
+  char *buffer;
+  size_t cursor;
+  size_t readfrom;  // if -1, no newline in buffer
+};
+
+// Returns false on EOF. FILE remains ownership of the caller.
+bool file_lines_open(const char *progname, const char *fname, FILE *f, struct file_lines *dst);
+
+// Returns whether successful
+bool file_lines_read(struct file_lines *fl, struct string_view *dst);
+
+void file_lines_close(struct file_lines *fl);