2 files changed, 195 insertions, 0 deletions
diff --git a/src/Path/Path.c b/src/Path/Path.c
new file mode 100644
index 0000000..8a0ab2b
--- /dev/null
+++ b/src/Path/Path.c
@@ -0,0 +1,185 @@
+#define _POSIX_C_SOURCE 200809L
+#define _XOPEN_SOURCE 700
+
+#include "Path/Path.h"
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+static const char output_prefix[] = "yapssg_";
+
+static int checked_add(size_t left, size_t right, size_t *sum) {
+  if (left > SIZE_MAX - right) {
+    return -1;
+  }
+  *sum = left + right;
+  return 0;
+}
+
+static char *duplicate_string(const char *value) {
+  size_t length = strlen(value);
+  char *copy = malloc(length + 1);
+
+  if (copy != NULL) {
+    memcpy(copy, value, length + 1);
+  }
+  return copy;
+}
+
+char *path_join(const char *left, const char *right) {
+  size_t left_length = strlen(left);
+  size_t right_length = strlen(right);
+  int needs_separator = left_length > 0 && left[left_length - 1] != '/';
+  size_t path_length;
+  size_t allocation_size;
+  char *path;
+
+  if (checked_add(left_length, (size_t)needs_separator, &path_length) != 0 ||
+      checked_add(path_length, right_length, &path_length) != 0 ||
+      checked_add(path_length, 1, &allocation_size) != 0) {
+    return NULL;
+  }
+
+  path = malloc(allocation_size);
+  if (path == NULL) {
+    return NULL;
+  }
+  memcpy(path, left, left_length);
+  if (needs_separator) {
+    path[left_length++] = '/';
+  }
+  memcpy(path + left_length, right, right_length + 1);
+  return path;
+}
+
+char *path_make_default_output(const char *input_path) {
+  const char *end = input_path + strlen(input_path);
+  const char *base;
+  size_t parent_length;
+  size_t base_length;
+  size_t prefix_length = sizeof(output_prefix) - 1;
+  size_t output_length;
+  size_t allocation_size;
+  char *output_path;
+
+  while (end > input_path + 1 && end[-1] == '/') {
+    --end;
+  }
+  base = end;
+  while (base > input_path && base[-1] != '/') {
+    --base;
+  }
+
+  parent_length = (size_t)(base - input_path);
+  base_length = (size_t)(end - base);
+  if (base_length == 0) {
+    return NULL;
+  }
+
+  if (checked_add(parent_length, prefix_length, &output_length) != 0 ||
+      checked_add(output_length, base_length, &output_length) != 0 ||
+      checked_add(output_length, 1, &allocation_size) != 0) {
+    return NULL;
+  }
+
+  output_path = malloc(allocation_size);
+  if (output_path == NULL) {
+    return NULL;
+  }
+  memcpy(output_path, input_path, parent_length);
+  memcpy(output_path + parent_length, output_prefix, prefix_length);
+  memcpy(output_path + parent_length + prefix_length, base, base_length);
+  output_path[parent_length + prefix_length + base_length] = '\0';
+  return output_path;
+}
+
+char *path_resolve_new(const char *path) {
+  char *path_copy = duplicate_string(path);
+  char *slash;
+  char *parent;
+  char *resolved_parent;
+  char *resolved_path;
+  const char *base;
+  size_t length;
+
+  if (path_copy == NULL) {
+    return NULL;
+  }
+
+  length = strlen(path_copy);
+  while (length > 1 && path_copy[length - 1] == '/') {
+    path_copy[--length] = '\0';
+  }
+
+  slash = strrchr(path_copy, '/');
+  if (slash == NULL) {
+    parent = duplicate_string(".");
+    base = path_copy;
+  } else if (slash == path_copy) {
+    parent = duplicate_string("/");
+    base = slash + 1;
+  } else {
+    *slash = '\0';
+    parent = duplicate_string(path_copy);
+    base = slash + 1;
+  }
+
+  if (parent == NULL || base[0] == '\0') {
+    free(parent);
+    free(path_copy);
+    return NULL;
+  }
+
+  resolved_parent = realpath(parent, NULL);
+  free(parent);
+  if (resolved_parent == NULL) {
+    free(path_copy);
+    return NULL;
+  }
+
+  resolved_path = path_join(resolved_parent, base);
+  free(resolved_parent);
+  free(path_copy);
+  return resolved_path;
+}
+
+char *path_resolve_from_file(const char *file_path, const char *relative_path) {
+  const char *slash;
+  size_t directory_length;
+  size_t relative_length;
+  size_t path_length;
+  size_t allocation_size;
+  char *path;
+
+  if (relative_path[0] == '/') {
+    return duplicate_string(relative_path);
+  }
+
+  slash = strrchr(file_path, '/');
+  directory_length = slash == NULL ? 0 : (size_t)(slash - file_path + 1);
+  relative_length = strlen(relative_path);
+  if (checked_add(directory_length, relative_length, &path_length) != 0 ||
+      checked_add(path_length, 1, &allocation_size) != 0) {
+    return NULL;
+  }
+
+  path = malloc(allocation_size);
+  if (path == NULL) {
+    return NULL;
+  }
+
+  memcpy(path, file_path, directory_length);
+  memcpy(path + directory_length, relative_path, relative_length + 1);
+  return path;
+}
+
+int path_is_within(const char *parent, const char *candidate) {
+  size_t parent_length = strlen(parent);
+
+  if (parent_length == 1 && parent[0] == '/') {
+    return candidate[0] == '/';
+  }
+  return strncmp(parent, candidate, parent_length) == 0 &&
+         (candidate[parent_length] == '\0' || candidate[parent_length] == '/');
+}
diff --git a/src/Path/Path.h b/src/Path/Path.h
new file mode 100644
index 0000000..a4ac530
--- /dev/null
+++ b/src/Path/Path.h
@@ -0,0 +1,10 @@
+#ifndef YAPSSG_PATH_H
+#define YAPSSG_PATH_H
+
+char *path_join(const char *left, const char *right);
+char *path_make_default_output(const char *input_path);
+char *path_resolve_new(const char *path);
+char *path_resolve_from_file(const char *file_path, const char *relative_path);
+int path_is_within(const char *parent, const char *candidate);
+
+#endif