enforce 16MB limit on predicate size (#80)

Signed-off-by: Brian DeHamer <[email protected]>

README.md

@@ -81,12 +81,14 @@ See [action.yml](action.yml)
     # URI identifying the type of the predicate.
     predicate-type:
 
-    # JSON string containing the value for the attestation predicate. Must
-    # supply exactly one of "predicate-path" or "predicate".
+    # String containing the value for the attestation predicate. String length
+    # cannot exceed 16MB. Must supply exactly one of "predicate-path" or
+    # "predicate".
     predicate:
 
-    # Path to the file which contains the JSON content for the attestation
-    # predicate. Must supply exactly one of "predicate-path" or "predicate".
+    # Path to the file which contains the content for the attestation predicate.
+    # File size cannot exceed 16MB. Must supply exactly one of "predicate-path"
+    # or "predicate".
     predicate-path:
 
     # Whether to push the attestation to the image registry. Requires that the
@@ -124,6 +126,11 @@ processed in batches 50. After the initial group of 50, each subsequent batch
 will incur an exponentially increasing amount of delay (capped at 1 minute of
 delay per batch) to avoid overwhelming the attestation API.
 
+### Predicate Limits
+
+Whether supplied via the `predicate` or `predicatePath` input, the predicate
+string cannot exceed 16MB.
+
 ## Examples
 
 ### Identify Subject by Path

__tests__/predicate.test.ts

@@ -78,6 +78,20 @@ describe('subjectFromInputs', () => {
     })
   })
 
+  describe('when specifying a predicate path that does not exist', () => {
+    const predicateType = 'https://example.com/predicate'
+    const predicatePath = 'foo'
+
+    it('returns the predicate', () => {
+      const inputs: PredicateInputs = {
+        ...blankInputs,
+        predicateType,
+        predicatePath
+      }
+      expect(() => predicateFromInputs(inputs)).toThrow(/file not found/)
+    })
+  })
+
   describe('when specifying a predicate value', () => {
     const predicateType = 'https://example.com/predicate'
     const content = '{}'
@@ -95,4 +109,21 @@ describe('subjectFromInputs', () => {
       })
     })
   })
+
+  describe('when specifying a predicate value exceeding the max size', () => {
+    const predicateType = 'https://example.com/predicate'
+    const content = JSON.stringify({ a: 'a'.repeat(16 * 1024 * 1024) })
+
+    it('throws an error', () => {
+      const inputs: PredicateInputs = {
+        ...blankInputs,
+        predicateType,
+        predicate: content
+      }
+
+      expect(() => predicateFromInputs(inputs)).toThrow(
+        /predicate string exceeds maximum/
+      )
+    })
+  })
 })

action.yml

@@ -30,13 +30,15 @@ inputs:
     required: true
   predicate:
     description: >
-      String containing the value for the attestation predicate. Must supply
-      exactly one of "predicate-path" or "predicate".
+      String containing the value for the attestation predicate. String length
+      cannot exceed 16MB. Must supply exactly one of "predicate-path" or
+      "predicate".
     required: false
   predicate-path:
     description: >
       Path to the file which contains the content for the attestation predicate.
-      Must supply exactly one of "predicate-path" or "predicate".
+      File size cannot exceed 16MB. Must supply exactly one of "predicate-path"
+      or "predicate".
     required: false
   push-to-registry:
     description: >

src/predicate.ts

@@ -7,6 +7,9 @@ export type PredicateInputs = {
   predicate: string
   predicatePath: string
 }
+
+const MAX_PREDICATE_SIZE_BYTES = 16 * 1024 * 1024
+
 // Returns the predicate specified by the action's inputs. The predicate value
 // may be specified as a path to a file or as a string.
 export const predicateFromInputs = (inputs: PredicateInputs): Predicate => {
@@ -24,9 +27,30 @@ export const predicateFromInputs = (inputs: PredicateInputs): Predicate => {
     throw new Error('Only one of predicate-path or predicate may be provided')
   }
 
-  const params = predicatePath
-    ? fs.readFileSync(predicatePath, 'utf-8')
-    : predicate
+  let params: string = predicate
+
+  if (predicatePath) {
+    if (!fs.existsSync(predicatePath)) {
+      throw new Error(`predicate file not found: ${predicatePath}`)
+    }
+
+    /* istanbul ignore next */
+    if (fs.statSync(predicatePath).size > MAX_PREDICATE_SIZE_BYTES) {
+      throw new Error(
+        `predicate file exceeds maximum allowed size: ${MAX_PREDICATE_SIZE_BYTES} bytes`
+      )
+    }
+
+    params = fs.readFileSync(predicatePath, 'utf-8')
+  } else {
+    if (predicate.length > MAX_PREDICATE_SIZE_BYTES) {
+      throw new Error(
+        `predicate string exceeds maximum allowed size: ${MAX_PREDICATE_SIZE_BYTES} bytes`
+      )
+    }
+
+    params = predicate
+  }
 
   return { type: predicateType, params: JSON.parse(params) }
 }