Lab report 2

Handling text after the last link

basic-link.md is the failure-inducing input that prompted me to make that change.

I ran java MarkdownParse.java basic-link.md.

The symptom of the bug involved a short wait time for it to run, followed by an uncaught runtime exception.

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
        at java.base/java.util.Arrays.copyOf(Arrays.java:3511)
        at java.base/java.util.Arrays.copyOf(Arrays.java:3480)
        at java.base/java.util.ArrayList.grow(ArrayList.java:237)
        at java.base/java.util.ArrayList.grow(ArrayList.java:244)
        at java.base/java.util.ArrayList.add(ArrayList.java:454)
        at java.base/java.util.ArrayList.add(ArrayList.java:467)
        at MarkdownParse.getLinks(MarkdownParse.java:18)
        at MarkdownParse.main(MarkdownParse.java:26)

The bug is that if currentIndex hadn’t reached the last character of markdown, the code would keep looking for links even when there weren’t any more; markdown.indexOf("[", currentIndex) would return -1, which brought currentIndex back to the beginning. This effectively caused an infinite loop, and since links are constantly being added to toReturn, the program eventually ran out of memory, resulting in the OutOfMemoryError symptom.

The failure-inducing input caused this symptom by having a single newline character after the link to prevent currentIndex from reaching the last character of markdown after the end of the link.

Handling parentheses in URLs

weird-urls.md is the failure-inducing input that prompted me to make that change.

I ran java MarkdownParse.java weird-urls.md.

The symptom of the bug was that the URL printed by the program omitted the closing parenthesis. This disagreed with how VS Code and GitHub rendered the link, which included the closing parenthesis in the URL.

[https://en.wikipedia.org/wiki/1984_(disambiguation]

It seems VS Code and GitHub match closing parentheses, i.e. if there’s a opening parenthesis in the URL, its corresponding closing parenthesis also belongs to the URL, as opposed to marking the end of the link URL.

For example, this Markdown link

[Wikipedia disambiguation page on disambiguation](https://en.wikipedia.org/wiki/Disambiguation_(disambiguation)))

is rendered as

Wikipedia disambiguation page on disambiguation)

with one closing parenthesis in the URL and a closing parenthesis as plain text after the link.

The bug is that the program found the first instance of ) after the opening parenthesis of the link in the Markdown, rather than trying to pair these parentheses, and took the contents in between the parentheses, excluding the parentheses, as the URL of the link. This results in the symptom—the outputted URL missing a closing parenthesis—because the program thought the closing parenthesis in (disambiguation) was the closing parenthesis of the link.

The failure-inducing input caused the symptom by having a pair of parentheses in the URL of a link.

Ensuring nothing between the ] and (

test-file5.md is the failure-inducing input that prompted me to make that change.

I ran javac -cp .:lib/junit-4.13.2.jar:lib/hamcrest-core-1.3.jar MarkdownParseTest.java && java -cp .:lib/junit-4.13.2.jar:lib/hamcrest-core-1.3.jar org.junit.runner.JUnitCore MarkdownParseTest.

The symptom of the bug is in the test output.

JUnit version 4.13.2
...........E.....
Time: 0.018
There was 1 failure:
1) testTestFile5(MarkdownParseTest)
java.lang.AssertionError: expected:<[]> but was:<[page.com]>
        at org.junit.Assert.fail(Assert.java:89)
        at org.junit.Assert.failNotEquals(Assert.java:835)
        at org.junit.Assert.assertEquals(Assert.java:120)
        at org.junit.Assert.assertEquals(Assert.java:146)
        at MarkdownParseTest.testTestFile5(MarkdownParseTest.java:45)

FAILURES!!!
Tests run: 16,  Failures: 1

The symptom is that getLinks was returning [page.com] instead of an empty list when given the contents of test-file5.md.

Running java MarkdownParse.java test-file5.md gives the following output.

[page.com]

However, VS Code and GitHub’s markdown renderers don’t render any links for test-file5.md.

The bug is because the program did not check if ] and ( in a possible link are adjacent. This caused the symptom because even though there was a paragraph between the square bracket and the parenthesis, it still thought [stuff]...(page.com) was a link and consequently added page.com to the list of links.

The failure-inducing input caused the symptom by having content between the closing bracket and the opening parenthesis.