Initial work, and name change to pantograph

1 files changed, 199 insertions, 0 deletions

diff --git a/libawl/src/sse.zig b/libawl/src/sse.zig
new file mode 100644
index 0000000..150c3ea
--- /dev/null
+++ b/libawl/src/sse.zig
@@ -0,0 +1,199 @@
+const std = @import("std");
+
+/// Parsed SSE event data — the content after "data: " (prefix removed).
+/// For multi-line data events, lines are joined with newlines per the SSE spec.
+///
+/// Borrowed from the parser's internal buffer. Call `SSEParser.freeEvents()`
+/// to free the events list when done (event data itself is borrowed and
+/// does not need individual freeing).
+const Event = []const u8;
+
+/// Incremental SSE line parser.
+///
+/// The HTTP client delivers arbitrary-sized read buffers; this module
+/// reassembles them into complete `data: ...\n\n` events.
+///
+/// Event data is borrowed from the internal buffer. Call `freeEvents()` to
+/// free the events list returned by `feed`; the event data itself is borrowed
+/// from the parser's buffer and does not need individual freeing.
+pub const SSEParser = struct {
+    buf: std.ArrayList(u8) = .empty,
+    allocator: std.mem.Allocator,
+
+    pub fn init(allocator: std.mem.Allocator) SSEParser {
+        return .{
+            .allocator = allocator,
+        };
+    }
+
+    /// Feed a chunk of raw bytes. Returns a list of complete SSE events
+    /// found in the buffer. Returns an empty list if no complete events
+    /// are available yet.
+    ///
+    /// Event data is borrowed from the internal buffer. Call `freeEvents()`
+    /// on the returned list when done.
+    pub fn feed(self: *SSEParser, chunk: []const u8) ![]Event {
+        try self.buf.appendSlice(self.allocator, chunk);
+
+        var events = std.ArrayList(Event).init(self.allocator);
+        errdefer events.deinit();
+
+        var write_pos: usize = 0;
+        var scan_pos: usize = 0;
+
+        while (std.mem.indexOf(u8, self.buf.items[scan_pos..], "\n\n")) |rel_delim| {
+            const delim = scan_pos + rel_delim;
+            const event_bytes = self.buf.items[scan_pos..delim];
+
+            // Compact data lines in-place. Compacted data is always shorter
+            // than the original event bytes (we strip at least "data: " per
+            // line), so write_pos <= scan_pos and we never overwrite data
+            // we haven't yet read.
+            const data_start = write_pos;
+            var line_start: usize = 0;
+            var has_data = false;
+
+            while (line_start < event_bytes.len) {
+                const newline = std.mem.indexOfScalarPos(u8, event_bytes, line_start, '\n') orelse event_bytes.len;
+                const line = event_bytes[line_start..newline];
+
+                if (std.mem.startsWith(u8, line, "data: ")) {
+                    if (has_data) {
+                        self.buf.items[write_pos] = '\n';
+                        write_pos += 1;
+                    }
+                    const content = line["data: ".len..];
+                    std.mem.copyForwards(u8, self.buf.items[write_pos .. write_pos + content.len], content);
+                    write_pos += content.len;
+                    has_data = true;
+                }
+                // Ignore other SSE fields (event:, id:, retry:) and comments (starting with :)
+
+                line_start = newline + 1;
+            }
+
+            if (has_data) {
+                try events.append(self.buf.items[data_start..write_pos]);
+            }
+
+            scan_pos = delim + 2;
+        }
+
+        // Shift remaining (incomplete) bytes to the front, retaining
+        // the backing allocation for reuse.
+        const remaining_len = self.buf.items.len - scan_pos;
+        if (remaining_len > 0 and scan_pos > 0) {
+            std.mem.copyForwards(u8, self.buf.items[0..remaining_len], self.buf.items[scan_pos..]);
+        }
+        self.buf.shrinkRetainingCapacity(remaining_len);
+
+        return events.toOwnedSlice();
+    }
+
+    /// Free a list of events returned by `feed`.
+    /// Event data is borrowed from the parser's buffer and does not need
+    /// to be freed individually; only the events array itself is freed.
+    pub fn freeEvents(self: *SSEParser, events: []Event) void {
+        self.allocator.free(events);
+    }
+
+    pub fn deinit(self: *SSEParser) void {
+        self.buf.deinit(self.allocator);
+    }
+};
+
+test "SSEParser - single complete event" {
+    const allocator = std.testing.allocator;
+
+    var parser = SSEParser.init(allocator);
+    defer parser.deinit();
+
+    const events = try parser.feed("data: hello\n\n");
+    defer parser.freeEvents(events);
+
+    try std.testing.expectEqual(@as(usize, 1), events.len);
+    try std.testing.expectEqualStrings("hello", events[0]);
+}
+
+test "SSEParser - partial then complete" {
+    const allocator = std.testing.allocator;
+
+    var parser = SSEParser.init(allocator);
+    defer parser.deinit();
+
+    // Feed partial — no complete event yet
+    const events1 = try parser.feed("data: hel");
+    defer parser.freeEvents(events1);
+    try std.testing.expectEqual(@as(usize, 0), events1.len);
+
+    // Feed remainder — completes the event
+    const events2 = try parser.feed("lo\n\n");
+    defer parser.freeEvents(events2);
+    try std.testing.expectEqual(@as(usize, 1), events2.len);
+    try std.testing.expectEqualStrings("hello", events2[0]);
+}
+
+test "SSEParser - multiple events in single chunk" {
+    const allocator = std.testing.allocator;
+
+    var parser = SSEParser.init(allocator);
+    defer parser.deinit();
+
+    const events = try parser.feed("data: one\n\ndata: two\n\n");
+    defer parser.freeEvents(events);
+
+    try std.testing.expectEqual(@as(usize, 2), events.len);
+    try std.testing.expectEqualStrings("one", events[0]);
+    try std.testing.expectEqualStrings("two", events[1]);
+}
+
+test "SSEParser - data DONE signal" {
+    const allocator = std.testing.allocator;
+
+    var parser = SSEParser.init(allocator);
+    defer parser.deinit();
+
+    const events = try parser.feed("data: [DONE]\n\n");
+    defer parser.freeEvents(events);
+
+    try std.testing.expectEqual(@as(usize, 1), events.len);
+    try std.testing.expectEqualStrings("[DONE]", events[0]);
+}
+
+test "SSEParser - empty event (keep-alive)" {
+    const allocator = std.testing.allocator;
+
+    var parser = SSEParser.init(allocator);
+    defer parser.deinit();
+
+    // A blank line (just \n\n) is a keep-alive comment with no data
+    const events = try parser.feed("\n\n");
+    defer parser.freeEvents(events);
+    try std.testing.expectEqual(@as(usize, 0), events.len);
+}
+
+test "SSEParser - ignores non-data fields" {
+    const allocator = std.testing.allocator;
+
+    var parser = SSEParser.init(allocator);
+    defer parser.deinit();
+
+    const events = try parser.feed("event: message\ndata: payload\nid: 42\n\n");
+    defer parser.freeEvents(events);
+
+    try std.testing.expectEqual(@as(usize, 1), events.len);
+    try std.testing.expectEqualStrings("payload", events[0]);
+}
+
+test "SSEParser - multi-line data joined with newline" {
+    const allocator = std.testing.allocator;
+
+    var parser = SSEParser.init(allocator);
+    defer parser.deinit();
+
+    const events = try parser.feed("data: line1\ndata: line2\n\n");
+    defer parser.freeEvents(events);
+
+    try std.testing.expectEqual(@as(usize, 1), events.len);
+    try std.testing.expectEqualStrings("line1\nline2", events[0]);
+}