The regular obfuscation process simply modifies some simple nodes, such
as identifiers and strings. In those cases, we modify the nodes
in-place, meaning that their positions remain the same. This hasn't
caused any problems.
Literal obfuscation is trickier. Since we replace one expression with an
entirely different one, we use cursor.Replace. The new expression is
entirely made up on the spot, so it lacks position information.
This was causing problems. For example, in the added test input:
> garble -literals build
[stderr]
# test/main
dgcm4t6w.go:3: misplaced compiler directive
dgcm4t6w.go:4: misplaced compiler directive
dgcm4t6w.go:3: misplaced compiler directive
dgcm4t6w.go:6: misplaced compiler directive
dgcm4t6w.go:7: misplaced compiler directive
dgcm4t6w.go:3: misplaced compiler directive
dgcm4t6w.go:9: misplaced compiler directive
dgcm4t6w.go:3: misplaced compiler directive
dgcm4t6w.go:3: too many errors
The build errors are because we'd move the compiler directives, which
makes the compiler unhappy as they must be directly followed by a
function declaration.
The root cause there seems to be that, since the replacement nodes lack
position information, go/printer would try to estimate its printing
position by adding to the last known position. Since -literals adds
code, this would result in the printer position increasing rapidly, and
potentially printing directive comments earlier than needed.
For now, making the replacement nodes have the same position as the
original node seems to stop go/printer from making this mistake.
It's possible that this workaround won't be bulletproof forever, but it
works well for now, and I don't see a simpler workaround right now.
It would be possible to use fancier mechanisms like go/ast.CommentMap or
dave/dst, but those are a significant amount of added complexity as well.
Fixes#285.
Fix up a few TODOs, and simplify the way we handle comments.
We now add whitespace around inline /*line*/ directives, to ensure we
don't break programs. A test case is added too.
We now add line directives to call sites, not function declarations,
since those are what actually shows up in stack traces.
It's unclear if we care about any other lines inside functions at all.
This also fixes reversing with -literals, since that feature adds a
significant amount of code which shuffles line numbers around.
Finally, we extend the tests with types, methods, and anonymous
functions, and we make all of them work well.
Updates #5.
In particular, the positions within function declarations, including the
positions of call sites to other functions.
Note that this isn't well tested just yet, particularly not with other
features like -literals. We can extend the tests and code over time.
This gets us the core basics.
The issue will be closed once the feature is documented for users, in a
follow-up PR.
Updates #5.
First, rename line_obfuscator.go to position.go. We obfuscate filenames,
not just line numbers, and "obfuscator" is a bit redundant.
Second, use "/*line :x*/" comments rather than the "//line :x" form, as
the former allows us to insert them in any position without adding
unnecessary newlines. This will be important for changing the position
of call sites, which will be important for "garble reverse".
Third, do not rely on go/ast to remove and add comments. Since they are
free-floating, we can very easily end up with misplaced comments,
especially as the literal obfuscator heavily modifies the AST.
The new method prints and re-parses the file, to ensure all node
positions are consistent with a buffer, buf1. Then, we copy the contents
into a new buffer, buf2, while inserting the comments that we need.
The new method also modifies line numbers at the very end of obfuscating
a Go file, instead of at the very beginning. That's going to be more
robust long-term, as we will also obfuscate line numbers for any
additions or modifications to the AST.
Fourth, detachedDirectives is unnecessary, as we can accomplish the same
with two simple prefix matches.
Finally, this means we can stop using detachedComments entirely, as
printFile already inserts the comments we need.
For #5.
Daniel Martí