Don't require a self link when parsing a RWPM (#555)

CHANGELOG.md

@@ -4,7 +4,14 @@ All notable changes to this project will be documented in this file. Take a look
 
 **Warning:** Features marked as *alpha* may change or be removed in a future release without notice. Use with caution.
 
-<!-- ## [Unreleased] -->
+## [Unreleased]
+
+### Changed
+
+#### Streamer
+
+* A `self` link is not required anymore when parsing a RWPM.
+
 
 ## [3.1.0]
 

Sources/Streamer/Parser/Readium/ReadiumWebPubParser.swift

@@ -55,8 +55,9 @@ public class ReadiumWebPubParser: PublicationParser, Loggable {
 
         return await resource.readAsRWPM(warnings: warnings)
             .flatMap { manifest in
-                guard let baseURL = manifest.baseURL else {
-                    return .failure(.decoding("No valid self link found in the manifest"))
+                let baseURL = manifest.baseURL
+                if baseURL == nil {
+                    warnings?.log(RWPMWarning(message: "No valid self link found in the manifest", severity: .moderate))
                 }
 
                 return .success(CompositeContainer(
@@ -165,3 +166,11 @@ private extension Streamable {
         }
     }
 }
+
+/// Warning raised when parsing a RWPM.
+public struct RWPMWarning: Warning {
+    public let message: String
+    public let severity: WarningSeverityLevel
+
+    public var tag: String { "rwpm" }
+}