tiny.content.Reader

1/// Read capability over one provider, for a holder that reopens bytes it2/// already has a reference for. The capability carries three things: the3/// capacity the store was built with, a function table whose single entry reads4/// by identifier, and an opaque context pointer borrowed from the provider that5/// produced it, so the provider outlives the Reader.6pub const Reader = struct {7    context: *anyopaque,8    capacity: model.Capacity,9    vtable: *const VTable,1011    pub const VTable: type = ReaderVTable;1213    /// Reopens the bytes of one reference into buffer storage the caller owns14    /// and returns the slice that was checked. The function rejects a reference15    /// whose extent is above the capacity's per-object byte limit, the *object16    /// ceiling*, with `ContentExtentExceeded` before it touches the provider,17    /// and it reports `CallerBufferTooSmall` when the buffer is shorter than18    /// the reference extent. The provider receives a slice cut to exactly that19    /// extent. The call reports `ContentTruncated` when the provider returns20    /// fewer bytes than the extent and `ContentExtentMismatch` when it returns21    /// more, and then rehashes what came back and reports22    /// `ContentIdentifierMismatch` when the digest disagrees, so a provider23    /// that returns the wrong bytes is caught here.24    pub fn read(25        self: Reader,26        reference: model.Reference,27        output: []u8,28    ) ReadError![]const u8 {29        try self.capacity.validateReference(reference);30        const expected = reference.extent.toUsize();31        if (output.len < expected) return error.CallerBufferTooSmall;32        const actual = try self.vtable.read(33            self.context,34            reference.identifier,35            output[0..expected],36        );37        if (actual < reference.extent.bytes) return error.ContentTruncated;38        if (actual > reference.extent.bytes) return error.ContentExtentMismatch;39        const verified = output[0..expected];40        if (!reference.identifier.matches(verified)) {41            return error.ContentIdentifierMismatch;42        }43        return verified;44    }45};

1pub const Reader = capability.Reader;