Linking to javadoc.io using Javadoc -link option

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野的像风
野的像风 2021-02-07 15:29

I am trying to link into some Javadocs hosted at javadoc.io (specifically, PowerMock\'s Javadocs) using the @link option. I have tried to add the URL to PowerMock\'

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  • 2021-02-07 15:57

    I have investigated the problem, the issue here is that a user agent must be set (an empty string is ok) in order for the connection to javadoc.io to complete successfully.

    I worked the problem around and wrote a Gradle plugin that may be of help for those who rely on that build system.

    Unfortunately, the work around can not get ported to the regular javadoc -link command invocation.

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  • 2021-02-07 16:01

    I am running javadoc.io.

    This is reported as this github issue and it's solved just now. There is no need to override user agent string any more.

    Feel free to re-open github issue if things are still not working. This thread is not actively monitored.

    curl -I -A "Java/1.6.0_14" https://static.javadoc.io/org.checkerframework/checker-qual/2.2.2/package-list
    HTTP/1.1 200 OK
    Date: Mon, 08 Apr 2019 13:06:04 GMT
    Content-Type: text/plain
    
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  • 2021-02-07 16:02

    It's strange: I could see in the browser e.g. http://static.javadoc.io/org.pegdown/pegdown/1.6.0/package-list but when I add http://static.javadoc.io/org.pegdown/pegdown/1.6.0 as javadoc's link option it says

    Error fetching URL: http://static.javadoc.io/org.pegdown/pegdown/1.6.0/package-list

    I use next workaround:

    1. With maven-dependency-plugin unapack the javadoc of desired dependency.
    2. Link it with linkoffline option.

      <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-dependency-plugin</artifactId>
          <version>2.8</version>
          <executions>
              <execution>
                  <id>unpack-javadoc</id>
                  <phase>package</phase>
                  <goals>
                      <goal>unpack</goal>
                  </goals>
                  <configuration>
                      <artifactItems>
                          <artifactItem>
                              <groupId>org.pegdown</groupId>
                              <artifactId>pegdown</artifactId>
                              <classifier>javadoc</classifier>
                              <version>${pegdownVersion}</version>
                              <overWrite>false</overWrite>
                              <outputDirectory>${project.build.directory}/pegdown-javadoc</outputDirectory>
                          </artifactItem>
                      </artifactItems>
                  </configuration>
              </execution>
          </executions>
      </plugin>
      <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-javadoc-plugin</artifactId>
          <configuration>
              <links>
                  <link>http://www.slf4j.org/apidocs/</link>
              </links>
              <offlineLinks>
                  <offlineLink>
                      <url>http://static.javadoc.io/org.pegdown/pegdown/${pegdownVersion}</url>
                      <location>${project.build.directory}/pegdown-javadoc</location>
                  </offlineLink>
              </offlineLinks>
          </configuration>
      </plugin>
      
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  • 2021-02-07 16:09

    I ended up just using -linkoffline to get around this issue, which I suppose has the nice property of not needing internet connectivity at build time, though if anyone has further thoughts on how to make this work with -link I'm all ears.

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  • 2021-02-07 16:10

    From the command line, use an argument like -J-Dhttp.agent=javadoc.

    In Maven, use something like:

    <additionalJOption>-J-Dhttp.agent=maven-javadoc-plugin-${pom‌​.name}</additionalJO‌​ption>

    The background: As Danilo Pianini suggests in another answer, the problem is the User-Agent header. However, the problem isn't an empty User-Agent; it's the default Java User-Agent, which looks something like "Java/1.8.0_112":

    $ URL=https://static.javadoc.io/org.checkerframework/checker-qual/2.2.2/package-list
    
    # default Java User-Agent:
    $ wget -U Java/1.8.0_112 "$URL" 2>&1 | grep response
    HTTP request sent, awaiting response... 403 Forbidden
    
    # no User-Agent:
    $ wget -U '' "$URL" 2>&1 | grep response
    HTTP request sent, awaiting response... 200 OK
    
    # custom User-Agent:
    $ wget -U javadoc "$URL" 2>&1 | grep response
    HTTP request sent, awaiting response... 200 OK
    

    So the fix is to tell Javadoc to use a different User-Agent. Java won't let you omit the User-Agent, so you'll have to provide a value, which Java will prepend to its default agent.

    As best I can tell, the blocking of Javadoc isn't intentional: Javadoc just (probably unwisely) uses the default Java User-Agent, and the content delivery network that javadoc.io uses blocks that by default.

    (One more note about Maven: Everything works fine with -link. It also works fine with -linkoffline if you download the package-list file and tell Javadoc to read it from disk. However, if you use -linkoffline but tell Javadoc to fetch package-list from the javadoc.io URL (this is an unusual thing to do), it may fail. The problem: Maven tries to pre-validate the package-list file but, under some versions of Java, fails because it rejects the SSL certificate of javadoc.io, a certificate that Javadoc itself accepts.)

    (Oh, and it appears to be important to use a URL specifically from static.javadoc.io, not javadoc.io. Also, I would recommend https, not http, in case http://static.javadoc.io someday starts issuing redirects to https://static.javadoc.io, as Javadoc currently doesn't handle such redirects. Also, https is a good thing :))

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