4 ms·

The reason that this function doesn't exist is that even if the sender sent a "message" in a single API call, there is no guarantee that the networking code wil

The reason that this function doesn't exist is that even if the sender sent a "message" in a single API call, there is no guarantee that the networking code will send it in one IP packet (or one layer 2 frame). We don't want to couple the message size with the lower network protocol, the type of network equipment and so on, and also want to allow merging of messages for more efficient use of the network (If we have a large window size it allows better throughput). So the job of separating the stream into messages is left to the application layer. (unlike for example in UDP, but then you have to worry about dropped messages)

SilasX 6y ago
What is that responding to? Of course TCP can split a message across multiple packets of the lower level protocol; that has no bearing on the concepts TCP works in and whether it can indicate end-of-message. If your point is just that TCP doesn't have a concept of a "message" (a bytestream with a clear beginning and ending), then that's fair, but, as I said elsewhere [1] the original comment took for granted that TCP does have a well defined notion of "you've reached the end of the message", or at least, "there is no further data to receive". No one seemed to have a problem with that there, and I was just working off that assumption. As before, I haven't checked whether this is true (I can't quickly verify from descriptions of TCP). And, interestingly enough, there's this comment [2], which says that what I described does exist, but isn't the default. So ... I'm at least not getting a consistent answer to my question, and people who think they know what they're talking about are inconsistent with each other. [1] https://news.ycombinator.com/item?id=23200293 https://news.ycombinator.com/item?id=23200293 [2] https://news.ycombinator.com/item?id=23200906 https://news.ycombinator.com/item?id=23200906
- deleted 6y ago
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- jacobolus 6y ago
  > the original comment took for granted that TCP does have a well defined notion of "you've reached the end of the message" No, the original comment was complaining about a coworker who didn’t understand (and refused to listen when told otherwise) that there is no such notion in TCP. It was a response to another comment complaining about people on the internet (e.g. Stack Overflow) too often making the same mistake. You’re more or less playing the part of that coworker here. It’s unclear why.
- yuribro 6y ago
  > Both of those seem (IMHO) like functions you could have in a TCP library. Neither seems (IMHO) like a higher level protocol. It's responding to the last part. It is a higher level of protocol. In the traditional TCP/IP model, it's in the application level. There are many libraries with an API like you asked, they are just in a higher level. (and TCP_WAITALL is a partial solution, applicable only if you know in advance the exact size of the message you are about to receive)

SilasX 6y ago

What is that responding to? Of course TCP can split a message across multiple packets of the lower level protocol; that has no bearing on the concepts TCP works in and whether it can indicate end-of-message. If your point is just that TCP doesn't have a concept of a "message" (a bytestream with a clear beginning and ending), then that's fair, but, as I said elsewhere [1] the original comment took for granted that TCP does have a well defined notion of "you've reached the end of the message", or at least, "there is no further data to receive". No one seemed to have a problem with that there, and I was just working off that assumption. As before, I haven't checked whether this is true (I can't quickly verify from descriptions of TCP). And, interestingly enough, there's this comment [2], which says that what I described does exist, but isn't the default. So ... I'm at least not getting a consistent answer to my question, and people who think they know what they're talking about are inconsistent with each other. [1] https://news.ycombinator.com/item?id=23200293 https://news.ycombinator.com/item?id=23200293 [2] https://news.ycombinator.com/item?id=23200906 https://news.ycombinator.com/item?id=23200906

deleted 6y ago
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jacobolus 6y ago
> the original comment took for granted that TCP does have a well defined notion of "you've reached the end of the message" No, the original comment was complaining about a coworker who didn’t understand (and refused to listen when told otherwise) that there is no such notion in TCP. It was a response to another comment complaining about people on the internet (e.g. Stack Overflow) too often making the same mistake. You’re more or less playing the part of that coworker here. It’s unclear why.
yuribro 6y ago
> Both of those seem (IMHO) like functions you could have in a TCP library. Neither seems (IMHO) like a higher level protocol. It's responding to the last part. It is a higher level of protocol. In the traditional TCP/IP model, it's in the application level. There are many libraries with an API like you asked, they are just in a higher level. (and TCP_WAITALL is a partial solution, applicable only if you know in advance the exact size of the message you are about to receive)