1 files changed, 103 insertions, 0 deletions
diff --git a/src/index.zig b/src/index.zig
new file mode 100644
index 0000000..7eb3e4b
--- /dev/null
+++ b/src/index.zig
@@ -0,0 +1,103 @@
+//! Discover Zig versions and their docs URLs from ziglang.org/download/index.json.
+
+const std = @import("std");
+const assert = std.debug.assert;
+const fetch = @import("fetch.zig");
+
+pub const index_url = "https://ziglang.org/download/index.json";
+
+/// Upper bound on versions we will process (NASA Power-of-10: bounded loops).
+pub const max_versions = 64;
+
+pub const Version = struct {
+    /// Release name as it appears in index.json (e.g. "master", "0.15.2").
+    name: []const u8,
+    /// Absolute URL of the single-page language reference.
+    docs_url: []const u8,
+};
+
+/// Owns the slice of versions and all their backing strings.
+pub const Versions = struct {
+    allocator: std.mem.Allocator,
+    items: []Version,
+
+    pub fn deinit(self: *Versions) void {
+        for (self.items) |v| {
+            self.allocator.free(v.name);
+            self.allocator.free(v.docs_url);
+        }
+        self.allocator.free(self.items);
+    }
+};
+
+/// Fetch and parse index.json, collecting every entry that has a `docs` URL.
+pub fn fetchAll(allocator: std.mem.Allocator, client: *std.http.Client) !Versions {
+    const json = try fetch.get(allocator, client, index_url);
+    defer allocator.free(json);
+    return parse(allocator, json);
+}
+
+/// Parse index.json bytes into owned versions. Split out for testability.
+pub fn parse(allocator: std.mem.Allocator, json: []const u8) !Versions {
+    assert(json.len > 0);
+
+    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, json, .{});
+    defer parsed.deinit();
+
+    const root = switch (parsed.value) {
+        .object => |o| o,
+        else => return error.MalformedIndex,
+    };
+
+    var list: std.ArrayList(Version) = .empty;
+    errdefer {
+        for (list.items) |v| {
+            allocator.free(v.name);
+            allocator.free(v.docs_url);
+        }
+        list.deinit(allocator);
+    }
+
+    var it = root.iterator();
+    while (it.next()) |entry| {
+        if (list.items.len >= max_versions) break;
+
+        const obj = switch (entry.value_ptr.*) {
+            .object => |o| o,
+            else => continue,
+        };
+        const docs = switch (obj.get("docs") orelse continue) {
+            .string => |s| s,
+            else => continue,
+        };
+        if (docs.len == 0) continue;
+
+        const name = try allocator.dupe(u8, entry.key_ptr.*);
+        errdefer allocator.free(name);
+        const url = try allocator.dupe(u8, docs);
+        try list.append(allocator, .{ .name = name, .docs_url = url });
+    }
+
+    return .{ .allocator = allocator, .items = try list.toOwnedSlice(allocator) };
+}
+
+test "parses versions with docs urls and skips entries without" {
+    const gpa = std.testing.allocator;
+    const json =
+        \\{
+        \\  "master": { "version": "0.16.0-dev", "docs": "https://ziglang.org/documentation/master/" },
+        \\  "0.15.2": { "docs": "https://ziglang.org/documentation/0.15.2/" },
+        \\  "0.1.0":  { "notes": "no docs here" }
+        \\}
+    ;
+    var versions = try parse(gpa, json);
+    defer versions.deinit();
+
+    try std.testing.expectEqual(@as(usize, 2), versions.items.len);
+    var saw_master = false;
+    for (versions.items) |v| {
+        try std.testing.expect(v.docs_url.len > 0);
+        if (std.mem.eql(u8, v.name, "master")) saw_master = true;
+    }
+    try std.testing.expect(saw_master);
+}