1 files changed, 243 insertions, 0 deletions
diff --git a/src/seekable_http_range.zig b/src/seekable_http_range.zig
new file mode 100644
index 0000000..059d1dd
--- /dev/null
+++ b/src/seekable_http_range.zig
@@ -0,0 +1,243 @@
+//! Reader/SeekableStream implementation of a resource over HTTP using Range requests.
+
+const std = @import("std");
+
+const SeekableHttpRange = @This();
+
+pub const Opts = struct {
+    allocator: std.mem.Allocator,
+    client: *std.http.Client,
+    url: []const u8,
+    buffer_size: usize = 1024,
+};
+
+allocator: std.mem.Allocator,
+client: *std.http.Client,
+url: []const u8,
+pos: u64 = 0,
+endpos: u64,
+buffer_pos: ?u64 = null,
+buffer: []u8,
+
+pub fn init(opts: Opts) !SeekableHttpRange {
+    var a = opts.allocator;
+    var client = opts.client;
+    var url = opts.url;
+    var res = try client.fetch(a, .{
+        .method = .HEAD,
+        .location = .{ .url = url },
+        .headers = std.http.Headers{ .allocator = a, .owned = false },
+    });
+    defer res.deinit();
+    if (res.status != .ok) return error.HttpStatusError;
+    const accept_header_val = res.headers.getFirstValue("accept-ranges") orelse return error.HttpRangeNotSpecified;
+    if (std.mem.eql(u8, accept_header_val, "none")) return error.HttpRangeNotSupported;
+    if (!std.mem.eql(u8, accept_header_val, "bytes")) return error.HttpRangeUnsupportedUnit;
+    const content_length_val = res.headers.getFirstValue("content-length") orelse return error.NoContentLength;
+    const content_length = std.fmt.parseInt(u64, content_length_val, 10) catch return error.ContentLengthFormatError;
+    var buffer = try a.alloc(u8, opts.buffer_size);
+    return .{
+        .allocator = opts.allocator,
+        .client = client,
+        .url = url,
+        .buffer = buffer,
+        .endpos = content_length,
+    };
+}
+
+pub fn deinit(self: *SeekableHttpRange) void {
+    self.allocator.free(self.buffer);
+}
+
+// it's a big list :(
+pub const ReadError = error{
+    UnsupportedHeader,
+    UnexpectedCharacter,
+    InvalidFormat,
+    InvalidPort,
+    OutOfMemory,
+    ConnectionRefused,
+    NetworkUnreachable,
+    ConnectionTimedOut,
+    ConnectionResetByPeer,
+    TemporaryNameServerFailure,
+    NameServerFailure,
+    UnknownHostName,
+    HostLacksNetworkAddresses,
+    UnexpectedConnectFailure,
+    TlsInitializationFailed,
+    UnsupportedUrlScheme,
+    UnexpectedWriteFailure,
+    InvalidContentLength,
+    UnsupportedTransferEncoding,
+    Overflow,
+    InvalidCharacter,
+    UriMissingHost,
+    CertificateBundleLoadFailure,
+    TlsFailure,
+    TlsAlert,
+    UnexpectedReadFailure,
+    EndOfStream,
+    HttpChunkInvalid,
+    SystemResources,
+    FileLocksNotSupported,
+    Unexpected,
+    AccessDenied,
+    NotWriteable,
+    MessageTooLong,
+    Unseekable,
+    InputOutput,
+    IsDir,
+    OperationAborted,
+    BrokenPipe,
+    NotOpenForReading,
+    NetNameDeleted,
+    WouldBlock,
+    MessageNotCompleted,
+    HttpHeadersExceededSizeLimit,
+    HttpHeadersInvalid,
+    HttpHeaderContinuationsUnsupported,
+    HttpTransferEncodingUnsupported,
+    HttpConnectionHeaderUnsupported,
+    CompressionNotSupported,
+    TooManyHttpRedirects,
+    RedirectRequiresResend,
+    HttpRedirectMissingLocation,
+    CompressionInitializationFailed,
+    DecompressionFailure,
+    InvalidTrailers,
+    StreamTooLong,
+    DiskQuota,
+    FileTooBig,
+    NoSpaceLeft,
+    DeviceBusy,
+    InvalidArgument,
+    NotOpenForWriting,
+    LockViolation,
+    HttpStatusError,
+    HttpNoBody,
+};
+
+pub const Reader = std.io.Reader(*SeekableHttpRange, ReadError, read);
+
+pub fn reader(self: *SeekableHttpRange) Reader {
+    return .{
+        .context = self,
+    };
+}
+
+pub fn read(self: *SeekableHttpRange, buffer: []u8) ReadError!usize {
+    var n: usize = 0;
+    for (0..buffer.len) |ix| {
+        const b = try readByte(self);
+        const bb = b orelse break;
+        buffer[ix] = bb;
+        n += 1;
+    }
+    return n;
+}
+
+fn readByte(self: *SeekableHttpRange) !?u8 {
+    if (self.pos >= self.endpos) return null;
+
+    if (self.buffer_pos) |buffer_pos| {
+        const buffer_end: u64 = buffer_pos + self.buffer.len;
+        if (self.pos >= buffer_pos and self.pos < buffer_end) {
+            return self.readFromBuffer();
+        }
+    }
+
+    // refill the buffer from pos
+    // max u64 formatted as decimal is 20 bytes long
+    const range_buf_len = "bytes=-".len + 20 + 20;
+    var range_buf = [_]u8{0} ** range_buf_len;
+    const nbuf_end = @min(self.pos + self.buffer.len, self.endpos);
+    // Range request end is _inclusive_
+    var range_value = std.fmt.bufPrint(&range_buf, "bytes={}-{}", .{ self.pos, nbuf_end - 1 }) catch unreachable;
+    var headers = std.http.Headers{ .allocator = self.allocator };
+    defer headers.deinit();
+    try headers.append("range", range_value);
+    var res = try self.client.fetch(self.allocator, .{
+        .location = .{ .url = self.url },
+        .headers = headers,
+    });
+    defer res.deinit();
+    if (res.status != .partial_content) return error.HttpStatusError;
+    const body = res.body orelse return error.HttpNoBody;
+    std.mem.copyForwards(u8, self.buffer, body);
+    self.buffer_pos = self.pos;
+    return self.readFromBuffer();
+}
+
+fn readFromBuffer(self: *SeekableHttpRange) u8 {
+    const pos_in_buffer = self.pos - self.buffer_pos.?;
+    defer self.pos += 1;
+    return self.buffer[pos_in_buffer];
+}
+
+pub const SeekError = error{};
+pub const GetSeekPosError = error{};
+pub const SeekableStream = std.io.SeekableStream(*SeekableHttpRange, SeekError, GetSeekPosError, seekTo, seekBy, getPos, getEndPos);
+
+pub fn seekableStream(self: *SeekableHttpRange) SeekableStream {
+    return .{
+        .context = self,
+    };
+}
+
+// copying from FixedBufferStream: clamp rather than return an error
+pub fn seekTo(self: *SeekableHttpRange, pos: u64) SeekError!void {
+    self.pos = std.math.clamp(pos, 0, self.endpos);
+}
+
+// copying from FixedBufferStream: clamp rather than return an error
+pub fn seekBy(self: *SeekableHttpRange, delta: i64) SeekError!void {
+    const np: u64 = if (std.math.sign(delta) == -1) 
+        std.math.sub(u64, self.pos, std.math.absCast(delta)) catch 0
+    else
+        std.math.add(u64, self.pos, std.math.absCast(delta)) catch std.math.maxInt(u64);
+    self.pos = std.math.clamp(np, 0, self.endpos);
+}
+
+pub fn getPos(self: *SeekableHttpRange) GetSeekPosError!u64 {
+    return self.pos;
+}
+
+pub fn getEndPos(self: *SeekableHttpRange) GetSeekPosError!u64 {
+    return self.endpos;
+}
+
+test "endBytes" {
+    const a = std.testing.allocator;
+    var client = std.http.Client{ .allocator = a };
+    defer client.deinit();
+    var range = try SeekableHttpRange.init(.{ .allocator = a, .client = &client, .url = "https://mfashby.net/posts.zip" });
+    defer range.deinit();
+    var ss = range.seekableStream();
+    var rr = range.reader();
+    
+    var buf = try a.alloc(u8, 20);
+    defer a.free(buf);
+
+    try ss.seekTo(try ss.getEndPos() - 20);
+    try rr.readNoEof(buf);
+    try std.testing.expectEqualSlices(u8, &[_]u8{ 0x05, 0x06, 0x00, 0x00, 0x00, 0x00, 0x31, 0x00, 0x31, 0x00, 0xFD, 0x11, 0x00, 0x00, 0xEE, 0xB7, 0x00, 0x00, 0x00, 0x00 }, buf);
+
+    try ss.seekBy(-300);
+    try rr.readNoEof(buf);
+    try std.testing.expectEqualSlices(u8, &[_]u8{ 0x00, 0x00, 0x00, 0x08, 0x00, 0xA1, 0x3A, 0x17, 0x57, 0x85, 0x9F, 0x53, 0xCE, 0x26, 0x05, 0x00, 0x00, 0x37, 0x0A, 0x00 }, buf);
+
+    try ss.seekTo(0);
+    try ss.seekBy(-1);
+    try std.testing.expectEqual(@as(u64, 0), try ss.getPos());
+
+    try ss.seekBy(std.math.minInt(i64));
+    try std.testing.expectEqual(@as(u64, 0), try ss.getPos());
+
+    try ss.seekTo(try ss.getEndPos());
+    try ss.seekBy(1);
+    try std.testing.expectEqual(try ss.getEndPos(), try ss.getPos());
+
+    try ss.seekBy(std.math.maxInt(i64));
+    try std.testing.expectEqual(try ss.getEndPos(), try ss.getPos());
+}