Implementing Services in Java

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5 Implementing Services
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The disadvantage of using GET is the limitation on URI length If the entry IDs are UUIDs or something similar, each ID will use 36 characters While these types of IDs are not common in normal Rails applications, UUIDs are used very often in distributed systems In fact, the vote system should probably not enforce that an entry ID be an integer It should be up to the entry system to decide whether it will use integer or string IDs URI length limits vary, depending on clients, servers, and proxies that exist between them Browsers often have the strictest limitations on URI length Internet Explorer has a limit of around 2 KB, while Firefox has a limit of 65 KB However, these service APIs will be used by other libraries and not in a browser address bar, so the GET request can be used with larger limits For the purposes of Ruby services, it makes sense to look at the settings for the two most popular web servers: Nginx and Apache Nginx has a default URI length limit that depends on the platform it is built on It is either 4 KB for 32-bit systems or 8 KB for 64-bit systems The default setting can be increased through the large_client_header_buffers setting (see http://wikinginxorg/ NginxHttpCoreModule#large_client_header_buffers) Apache has a default URI length of 8190 bytes This default can be increased through the LimitRequestLine directive (see http://httpdapacheorg/docs/22/mod/corehtml#limitrequestline) The potential limitations are worth keeping in mind if the API is expected to handle many IDs in a single request The API should be able to return the vote values for a single entry and for a single entry and user (in addition to the multi-get versions) Instead of implementing separate calls for the single gets, the multi-get interface can be reused The request will simply have a list containing only one ID, and the response will have a list of results with only one element Limiting the total number of endpoints in an API will make it easier to program against, test, and modify Responses for an API should follow a predictable convention There are many different ways to return responses to multi-get requests One response format could return a JSON array of objects where the order is the same as the IDs requested The other option is to return a JSON hash with the ID as a key and the response as a value The latter option is a little more verbose, but it s more explicit and easier to handle in the client code
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The Vote Interface
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The final API decision to be made is what the interface for creating a vote should look like There are many valid ways to expose this functionality The only requirement is that the back-end server logic enforce the one vote per entry per user rule
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The Vote Service
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The data that must be conveyed is the entry ID, the user ID, and the vote value (up or down) There aren t any hard rules for the interface The decision really boils down to aesthetics Let s explore some of the possible interfaces to see which might be the most sensible:
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Option 1: REQUEST POST /api/v1/votes REQUEST BODY: { "user_id" : 3, "entry_id" : 45, "vote" : 1 } Option 2: REQUEST POST /api/v1/votes/entries/45 REQUEST BODY: { "user_id" : 3, "vote" : "up" } Option 3: REQUEST POST /api/v1/votes/entries/45/users/3 REQUEST BODY: { "vote" : -1 } Option 4: REQUEST POST /api/v1/votes/entries/45/up REQUEST BODY: { "user_id" : 3 }
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5 Implementing Services Option 5: REQUEST PUT /api/v1/votes/entries/45/users/3/vote_up Option 6: REQUEST PUT /api/v1/votes/entries/45/users/3 REQUEST BODY: { "value": "up" } Option 7: REQUEST POST /api/v1/votes/entries/45 REQUEST BODY: { "user_id" : 3, "value" : "up" }
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Each of these options uses a different combination of specifying the data in the URI and in the request body The options also use different HTTP methods and values for the vote The options highlight the three decisions that must be made when designing the vote interface: How should the vote value be represented What data should be specified in the URI or the request body Which HTTP method should be used The vote value could be represented as a string of up or down, or it could be represented as an integer value of 1 or 1 From a math perspective, the 1 and 1 values are appealing They can be added together, and they use fewer characters for transmitting the actual vote value The up and down values provide a little more readability The words also have symmetry It s intuitive that if you see up as a vote value, you can assume that down is the other one With a value of 1 you might wonder if 0, 1, or any other integer values are valid Finally, using up or down keeps you from attempting to add the values passed in from the API call, which could introduce bugs What if someone posts a vote value of 100 The server will have to make sure to bounds check the values When you use up and down, it s already known
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