Expand expansion map to support calling when a relative IRI is detected

lib/context.js

@@ -1041,19 +1041,88 @@ function _expandIri(activeCtx, value, relativeTo, localCtx, defined, options) {
     }
   }
 
-  // prepend vocab
   if(relativeTo.vocab && '@vocab' in activeCtx) {
-    return activeCtx['@vocab'] + value;
-  }
+    // prepend vocab
+    const prependedResult = activeCtx['@vocab'] + value;
+    let expansionMapResult = undefined;
+    if(options && options.expansionMap) {
+      // if we are about to expand the value by prepending
+      // @vocab then call the expansion map to inform
+      // interested callers that this is occurring
+
+      // TODO: use `await` to support async
+      expansionMapResult = options.expansionMap({
+        prependedIri: {
+          type: '@vocab',
+          vocab: activeCtx['@vocab'],
+          value,
+          result: prependedResult
+        },
+        activeCtx,
+        options
+      });
 
-  // prepend base
-  if(relativeTo.base && '@base' in activeCtx) {
-    if(activeCtx['@base']) {
-      // The null case preserves value as potentially relative
-      return prependBase(prependBase(options.base, activeCtx['@base']), value);
+    }
+    if(expansionMapResult !== undefined) {
+      value = expansionMapResult;
+    } else {
+      // the null case preserves value as potentially relative
+      value = prependedResult;
     }
   } else if(relativeTo.base) {
-    return prependBase(options.base, value);
+    // prepend base
+    let prependedResult;
+    let expansionMapResult;
+    let base;
+    if('@base' in activeCtx) {
+      if(activeCtx['@base']) {
+        base = prependBase(options.base, activeCtx['@base']);
+        prependedResult = prependBase(base, value);
+      }
+    } else {
+      base = options.base;
+      prependedResult = prependBase(options.base, value);
+    }
+    if(options && options.expansionMap) {
+      // if we are about to expand the value by pre-pending
+      // @base then call the expansion map to inform
+      // interested callers that this is occurring
+
+      // TODO: use `await` to support async
+      expansionMapResult = options.expansionMap({
+        prependedIri: {
+          type: '@base',
+          base,
+          value,
+          result: prependedResult
+        },
+        activeCtx,
+        options
+      });
+    }
+    if(expansionMapResult !== undefined) {
+      value = expansionMapResult;
+    } else if(prependedResult !== undefined) {
+      // the null case preserves value as potentially relative
+      value = prependedResult;
+    }
+  }
+
+  if(!_isAbsoluteIri(value) && options && options.expansionMap) {
+    // if the result of the expansion is not an absolute iri then
+    // call the expansion map to inform interested callers that
+    // the resulting value is a relative iri, which can result in
+    // it being dropped when converting to other RDF representations
+
+    // TODO: use `await` to support async
+    const expandedResult = options.expansionMap({
+      relativeIri: value,
+      activeCtx,
+      options
+    });
+    if(expandedResult !== undefined) {
+      value = expandedResult;
+    }
   }
 
   return value;

lib/expand.js

@@ -75,6 +75,10 @@ api.expand = async ({
   typeScopedContext = null,
   expansionMap = () => undefined
 }) => {
+
+  // add expansion map to the processing options
+  options = {...options, expansionMap};
+
   // nothing to expand
   if(element === null || element === undefined) {
     return null;
@@ -420,6 +424,9 @@ async function _expandObject({
   const nests = [];
   let unexpandedValue;
 
+  // add expansion map to the processing options
+  options = {...options, expansionMap};
+
   // Figure out if this is the type for a JSON literal
   const isJsonType = element[typeKey] &&
     _expandIri(activeCtx,

lib/util.js

@@ -130,7 +130,7 @@ api.parseLinkHeader = header => {
     while((match = REGEX_LINK_HEADER_PARAMS.exec(params))) {
       result[match[1]] = (match[2] === undefined) ? match[3] : match[2];
     }
-    const rel = result['rel'] || '';
+    const rel = result.rel || '';
     if(Array.isArray(rval[rel])) {
       rval[rel].push(result);
     } else if(rval.hasOwnProperty(rel)) {